Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.31   12.262%   $206.9101   $206.91   $206.90   $206.90  
  Purchase #2 $167.98   12.470%   $188.9271   $188.93   $188.95   $188.90  
  Purchase #3 $203.58   10.809%   $225.585   $225.59   $225.60   $225.60  
  Purchase #4 $91.56   10.409%   $101.0905   $101.09   $101.10   $101.10  
  Purchase #5 $164.77   11.849%   $184.2936   $184.29   $184.30   $184.30  
  Purchase #6 $152.72   11.639%   $170.4951   $170.50   $170.50   $170.50  
  Purchase #7 $154.64   9.230%   $168.9133   $168.91   $168.90   $168.90  
  7 purchase totals = $1,119.56       $1,246.2147   $1,246.22   $1,246.25   $1,246.20