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 $71.72   4.599%   $75.0184   $75.02   $75.00   $75.00  
  Purchase #2 $89.87   4.137%   $93.5879   $93.59   $93.60   $93.60  
  Purchase #3 $95.59   6.210%   $101.5261   $101.53   $101.55   $101.50  
  Purchase #4 $15.74   5.606%   $16.6224   $16.62   $16.60   $16.60  
  Purchase #5 $136.36   12.211%   $153.0109   $153.01   $153.00   $153.00  
  Purchase #6 $204.84   5.149%   $215.3872   $215.39   $215.40   $215.40  
  Purchase #7 $126.53   9.472%   $138.5149   $138.51   $138.50   $138.50  
  7 purchase totals = $740.65       $793.6678   $793.67   $793.65   $793.60