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 $206.80   12.620%   $232.8982   $232.90   $232.90   $232.90  
  Purchase #2 $136.61   7.572%   $146.9541   $146.95   $146.95   $147.00  
  Purchase #3 $170.52   10.663%   $188.7025   $188.70   $188.70   $188.70  
  Purchase #4 $17.96   10.763%   $19.893   $19.89   $19.90   $19.90  
  Purchase #5 $62.80   10.133%   $69.1635   $69.16   $69.15   $69.20  
  Purchase #6 $78.33   8.469%   $84.9638   $84.96   $84.95   $85.00  
  Purchase #7 $188.39   11.327%   $209.7289   $209.73   $209.75   $209.70  
  7 purchase totals = $861.41       $952.3040   $952.29   $952.30   $952.40