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 $60.26   10.703%   $66.7096   $66.71   $66.70   $66.70  
  Purchase #2 $55.81   12.461%   $62.7645   $62.76   $62.75   $62.80  
  Purchase #3 $165.91   4.271%   $172.996   $173.00   $173.00   $173.00  
  Purchase #4 $37.57   12.325%   $42.2005   $42.20   $42.20   $42.20  
  Purchase #5 $225.97   8.863%   $245.9977   $246.00   $246.00   $246.00  
  Purchase #6 $89.31   6.210%   $94.8562   $94.86   $94.85   $94.90  
  Purchase #7 $97.46   11.654%   $108.818   $108.82   $108.80   $108.80  
  7 purchase totals = $732.29       $794.3425   $794.35   $794.30   $794.40