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 $58.67   12.402%   $65.9463   $65.95   $65.95   $65.90  
  Purchase #2 $126.86   3.244%   $130.9753   $130.98   $131.00   $131.00  
  Purchase #3 $24.89   13.707%   $28.3017   $28.30   $28.30   $28.30  
  Purchase #4 $86.84   11.851%   $97.1314   $97.13   $97.15   $97.10  
  Purchase #5 $242.53   8.768%   $263.795   $263.80   $263.80   $263.80  
  Purchase #6 $23.88   5.809%   $25.2672   $25.27   $25.25   $25.30  
  Purchase #7 $190.95   9.379%   $208.8592   $208.86   $208.85   $208.90  
  7 purchase totals = $754.62       $820.2761   $820.29   $820.30   $820.30