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 $41.37   8.208%   $44.7656   $44.77   $44.75   $44.80  
  Purchase #2 $179.37   8.138%   $193.9671   $193.97   $193.95   $194.00  
  Purchase #3 $191.82   5.603%   $202.5677   $202.57   $202.55   $202.60  
  Purchase #4 $167.85   11.797%   $187.6513   $187.65   $187.65   $187.70  
  Purchase #5 $122.62   10.857%   $135.9329   $135.93   $135.95   $135.90  
  Purchase #6 $11.38   8.542%   $12.3521   $12.35   $12.35   $12.40  
  Purchase #7 $220.75   3.725%   $228.9729   $228.97   $228.95   $229.00  
  7 purchase totals = $935.16       $1,006.2096   $1,006.21   $1,006.15   $1,006.40