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 $134.59   12.157%   $150.9521   $150.95   $150.95   $151.00  
  Purchase #2 $199.67   9.870%   $219.3774   $219.38   $219.40   $219.40  
  Purchase #3 $26.47   12.310%   $29.7285   $29.73   $29.75   $29.70  
  Purchase #4 $221.90   6.662%   $236.683   $236.68   $236.70   $236.70  
  Purchase #5 $214.66   12.835%   $242.2116   $242.21   $242.20   $242.20  
  Purchase #6 $5.69   4.401%   $5.9404   $5.94   $5.95   $5.90  
  Purchase #7 $46.54   4.147%   $48.47   $48.47   $48.45   $48.50  
  7 purchase totals = $849.52       $933.3630   $933.36   $933.40   $933.40