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 $187.63   7.415%   $201.5428   $201.54   $201.55   $201.50  
  Purchase #2 $84.59   9.217%   $92.3867   $92.39   $92.40   $92.40  
  Purchase #3 $233.46   9.248%   $255.0504   $255.05   $255.05   $255.10  
  Purchase #4 $41.67   7.840%   $44.9369   $44.94   $44.95   $44.90  
  Purchase #5 $70.37   5.575%   $74.2931   $74.29   $74.30   $74.30  
  Purchase #6 $159.40   8.820%   $173.4591   $173.46   $173.45   $173.50  
  Purchase #7 $107.89   7.715%   $116.2137   $116.21   $116.20   $116.20  
  7 purchase totals = $885.01       $957.8827   $957.88   $957.90   $957.90