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 $46.49   5.838%   $49.2041   $49.20   $49.20   $49.20  
  Purchase #2 $221.26   11.152%   $245.9349   $245.93   $245.95   $245.90  
  Purchase #3 $113.38   9.378%   $124.0128   $124.01   $124.00   $124.00  
  Purchase #4 $215.33   6.206%   $228.6934   $228.69   $228.70   $228.70  
  Purchase #5 $23.45   11.348%   $26.1111   $26.11   $26.10   $26.10  
  Purchase #6 $75.77   10.802%   $83.9547   $83.95   $83.95   $84.00  
  Purchase #7 $168.90   8.858%   $183.8612   $183.86   $183.85   $183.90  
  7 purchase totals = $864.58       $941.7722   $941.75   $941.75   $941.80