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 $67.25   8.760%   $73.1411   $73.14   $73.15   $73.10  
  Purchase #2 $93.67   11.597%   $104.5329   $104.53   $104.55   $104.50  
  Purchase #3 $143.46   4.435%   $149.8225   $149.82   $149.80   $149.80  
  Purchase #4 $241.65   9.168%   $263.8045   $263.80   $263.80   $263.80  
  Purchase #5 $150.73   6.870%   $161.0852   $161.09   $161.10   $161.10  
  Purchase #6 $182.90   11.362%   $203.6811   $203.68   $203.70   $203.70  
  Purchase #7 $59.76   4.110%   $62.2161   $62.22   $62.20   $62.20  
  7 purchase totals = $939.42       $1,018.2834   $1,018.28   $1,018.30   $1,018.20