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 $189.64   3.107%   $195.5321   $195.53   $195.55   $195.50  
  Purchase #2 $77.42   11.544%   $86.3574   $86.36   $86.35   $86.40  
  Purchase #3 $108.42   10.409%   $119.7054   $119.71   $119.70   $119.70  
  Purchase #4 $64.44   12.515%   $72.5047   $72.50   $72.50   $72.50  
  Purchase #5 $248.45   12.331%   $279.0864   $279.09   $279.10   $279.10  
  Purchase #6 $24.69   8.843%   $26.8733   $26.87   $26.85   $26.90  
  Purchase #7 $178.69   5.457%   $188.4411   $188.44   $188.45   $188.40  
  7 purchase totals = $891.75       $968.5004   $968.50   $968.50   $968.50