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 $68.97   8.146%   $74.5883   $74.59   $74.60   $74.60  
  Purchase #2 $70.98   7.139%   $76.0473   $76.05   $76.05   $76.00  
  Purchase #3 $126.62   9.556%   $138.7198   $138.72   $138.70   $138.70  
  Purchase #4 $58.37   11.187%   $64.8999   $64.90   $64.90   $64.90  
  Purchase #5 $178.43   11.601%   $199.1297   $199.13   $199.15   $199.10  
  Purchase #6 $75.51   8.492%   $81.9223   $81.92   $81.90   $81.90  
  Purchase #7 $64.59   6.822%   $68.9963   $69.00   $69.00   $69.00  
  7 purchase totals = $643.47       $704.3036   $704.31   $704.30   $704.20