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 $241.43   12.262%   $271.0341   $271.03   $271.05   $271.00  
  Purchase #2 $63.43   6.585%   $67.6069   $67.61   $67.60   $67.60  
  Purchase #3 $154.59   10.353%   $170.5947   $170.59   $170.60   $170.60  
  Purchase #4 $227.40   10.495%   $251.2656   $251.27   $251.25   $251.30  
  Purchase #5 $154.43   6.487%   $164.4479   $164.45   $164.45   $164.40  
  Purchase #6 $207.96   4.113%   $216.5134   $216.51   $216.50   $216.50  
  Purchase #7 $60.91   9.427%   $66.652   $66.65   $66.65   $66.70  
  7 purchase totals = $1,110.15       $1,208.1146   $1,208.11   $1,208.10   $1,208.10