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 $65.38   4.499%   $68.3214   $68.32   $68.30   $68.30  
  Purchase #2 $150.63   12.169%   $168.9602   $168.96   $168.95   $169.00  
  Purchase #3 $59.29   5.571%   $62.593   $62.59   $62.60   $62.60  
  Purchase #4 $94.62   12.629%   $106.5696   $106.57   $106.55   $106.60  
  Purchase #5 $69.88   5.466%   $73.6996   $73.70   $73.70   $73.70  
  Purchase #6 $115.50   8.592%   $125.4238   $125.42   $125.40   $125.40  
  Purchase #7 $135.89   10.816%   $150.5879   $150.59   $150.60   $150.60  
  7 purchase totals = $691.19       $756.1555   $756.15   $756.10   $756.20