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 $83.48   10.574%   $92.3072   $92.31   $92.30   $92.30  
  Purchase #2 $243.59   7.281%   $261.3258   $261.33   $261.35   $261.30  
  Purchase #3 $143.41   9.817%   $157.4886   $157.49   $157.50   $157.50  
  Purchase #4 $209.97   10.438%   $231.8867   $231.89   $231.90   $231.90  
  Purchase #5 $242.71   12.407%   $272.823   $272.82   $272.80   $272.80  
  Purchase #6 $203.38   7.175%   $217.9725   $217.97   $217.95   $218.00  
  Purchase #7 $168.67   13.806%   $191.9566   $191.96   $191.95   $192.00  
  7 purchase totals = $1,295.21       $1,425.7604   $1,425.77   $1,425.75   $1,425.80