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 $177.71   8.769%   $193.2934   $193.29   $193.30   $193.30  
  Purchase #2 $186.80   8.854%   $203.3393   $203.34   $203.35   $203.30  
  Purchase #3 $58.43   6.378%   $62.1567   $62.16   $62.15   $62.20  
  Purchase #4 $100.98   11.701%   $112.7957   $112.80   $112.80   $112.80  
  Purchase #5 $183.65   5.742%   $194.1952   $194.20   $194.20   $194.20  
  Purchase #6 $99.71   5.654%   $105.3476   $105.35   $105.35   $105.30  
  Purchase #7 $132.95   6.726%   $141.8922   $141.89   $141.90   $141.90  
  7 purchase totals = $940.23       $1,013.0201   $1,013.03   $1,013.05   $1,013.00