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 $57.31   9.593%   $62.8077   $62.81   $62.80   $62.80  
  Purchase #2 $133.51   12.317%   $149.9544   $149.95   $149.95   $150.00  
  Purchase #3 $159.52   6.221%   $169.4437   $169.44   $169.45   $169.40  
  Purchase #4 $195.36   9.268%   $213.466   $213.47   $213.45   $213.50  
  Purchase #5 $179.46   4.369%   $187.3006   $187.30   $187.30   $187.30  
  Purchase #6 $222.75   12.309%   $250.1683   $250.17   $250.15   $250.20  
  Purchase #7 $124.38   6.370%   $132.303   $132.30   $132.30   $132.30  
  7 purchase totals = $1,072.29       $1,165.4437   $1,165.44   $1,165.40   $1,165.50