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 $53.41   13.501%   $60.6209   $60.62   $60.60   $60.60  
  Purchase #2 $92.38   10.137%   $101.7446   $101.74   $101.75   $101.70  
  Purchase #3 $247.37   4.302%   $258.0119   $258.01   $258.00   $258.00  
  Purchase #4 $91.66   6.398%   $97.5244   $97.52   $97.50   $97.50  
  Purchase #5 $9.63   7.435%   $10.346   $10.35   $10.35   $10.30  
  Purchase #6 $22.55   10.594%   $24.9389   $24.94   $24.95   $24.90  
  Purchase #7 $47.58   10.616%   $52.6311   $52.63   $52.65   $52.60  
  7 purchase totals = $564.58       $605.8178   $605.81   $605.80   $605.60