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 $84.52   9.107%   $92.2172   $92.22   $92.20   $92.20  
  Purchase #2 $240.91   4.123%   $250.8427   $250.84   $250.85   $250.80  
  Purchase #3 $208.75   11.491%   $232.7375   $232.74   $232.75   $232.70  
  Purchase #4 $70.74   3.396%   $73.1423   $73.14   $73.15   $73.10  
  Purchase #5 $57.56   5.172%   $60.537   $60.54   $60.55   $60.50  
  Purchase #6 $139.68   13.597%   $158.6723   $158.67   $158.65   $158.70  
  Purchase #7 $64.27   11.538%   $71.6855   $71.69   $71.70   $71.70  
  7 purchase totals = $866.43       $939.8345   $939.84   $939.85   $939.70