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 $29.84   8.763%   $32.4549   $32.45   $32.45   $32.50  
  Purchase #2 $205.77   9.622%   $225.5692   $225.57   $225.55   $225.60  
  Purchase #3 $58.75   10.548%   $64.947   $64.95   $64.95   $64.90  
  Purchase #4 $91.75   13.692%   $104.3124   $104.31   $104.30   $104.30  
  Purchase #5 $238.76   6.811%   $255.0219   $255.02   $255.00   $255.00  
  Purchase #6 $126.59   9.618%   $138.7654   $138.77   $138.75   $138.80  
  Purchase #7 $75.73   9.779%   $83.1356   $83.14   $83.15   $83.10  
  7 purchase totals = $827.19       $904.2064   $904.21   $904.15   $904.20