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 $47.44   9.706%   $52.0445   $52.04   $52.05   $52.00  
  Purchase #2 $202.48   7.342%   $217.3461   $217.35   $217.35   $217.30  
  Purchase #3 $59.46   13.512%   $67.4942   $67.49   $67.50   $67.50  
  Purchase #4 $104.56   11.717%   $116.8113   $116.81   $116.80   $116.80  
  Purchase #5 $48.48   12.830%   $54.7   $54.70   $54.70   $54.70  
  Purchase #6 $187.50   9.117%   $204.5944   $204.59   $204.60   $204.60  
  Purchase #7 $184.28   13.347%   $208.8759   $208.88   $208.90   $208.90  
  7 purchase totals = $834.20       $921.8664   $921.86   $921.90   $921.80