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 $245.47   8.845%   $267.1818   $267.18   $267.20   $267.20  
  Purchase #2 $187.73   6.168%   $199.3092   $199.31   $199.30   $199.30  
  Purchase #3 $60.84   7.753%   $65.5569   $65.56   $65.55   $65.60  
  Purchase #4 $94.62   10.361%   $104.4236   $104.42   $104.40   $104.40  
  Purchase #5 $187.90   6.496%   $200.106   $200.11   $200.10   $200.10  
  Purchase #6 $110.78   12.822%   $124.9842   $124.98   $125.00   $125.00  
  Purchase #7 $187.36   4.209%   $195.246   $195.25   $195.25   $195.20  
  7 purchase totals = $1,074.70       $1,156.8077   $1,156.81   $1,156.80   $1,156.80