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 $153.78   10.452%   $169.8531   $169.85   $169.85   $169.90  
  Purchase #2 $182.97   3.193%   $188.8122   $188.81   $188.80   $188.80  
  Purchase #3 $246.36   6.748%   $262.9844   $262.98   $263.00   $263.00  
  Purchase #4 $95.31   4.286%   $99.395   $99.40   $99.40   $99.40  
  Purchase #5 $106.36   12.663%   $119.8284   $119.83   $119.85   $119.80  
  Purchase #6 $244.97   12.791%   $276.3041   $276.30   $276.30   $276.30  
  Purchase #7 $216.43   5.526%   $228.3899   $228.39   $228.40   $228.40  
  7 purchase totals = $1,246.18       $1,345.5671   $1,345.56   $1,345.60   $1,345.60