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 $209.66   10.667%   $232.0244   $232.02   $232.00   $232.00  
  Purchase #2 $173.73   4.824%   $182.1107   $182.11   $182.10   $182.10  
  Purchase #3 $221.60   13.339%   $251.1592   $251.16   $251.15   $251.20  
  Purchase #4 $210.52   3.771%   $218.4587   $218.46   $218.45   $218.50  
  Purchase #5 $93.67   4.801%   $98.1671   $98.17   $98.15   $98.20  
  Purchase #6 $222.86   9.811%   $244.7248   $244.72   $244.70   $244.70  
  Purchase #7 $79.98   9.184%   $87.3254   $87.33   $87.35   $87.30  
  7 purchase totals = $1,212.02       $1,313.9703   $1,313.97   $1,313.90   $1,314.00