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 $68.86   10.443%   $76.051   $76.05   $76.05   $76.10  
  Purchase #2 $9.93   6.370%   $10.5625   $10.56   $10.55   $10.60  
  Purchase #3 $51.95   12.659%   $58.5264   $58.53   $58.55   $58.50  
  Purchase #4 $59.77   5.149%   $62.8476   $62.85   $62.85   $62.80  
  Purchase #5 $33.52   7.206%   $35.9355   $35.94   $35.95   $35.90  
  Purchase #6 $148.54   9.298%   $162.3512   $162.35   $162.35   $162.40  
  Purchase #7 $212.59   7.700%   $228.9594   $228.96   $228.95   $229.00  
  7 purchase totals = $585.16       $635.2336   $635.24   $635.25   $635.30