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 $95.30   13.164%   $107.8453   $107.85   $107.85   $107.80  
  Purchase #2 $169.63   11.378%   $188.9305   $188.93   $188.95   $188.90  
  Purchase #3 $35.64   11.486%   $39.7336   $39.73   $39.75   $39.70  
  Purchase #4 $155.58   13.603%   $176.7435   $176.74   $176.75   $176.70  
  Purchase #5 $43.45   11.175%   $48.3055   $48.31   $48.30   $48.30  
  Purchase #6 $48.75   9.786%   $53.5207   $53.52   $53.50   $53.50  
  Purchase #7 $133.47   8.256%   $144.4893   $144.49   $144.50   $144.50  
  7 purchase totals = $681.82       $759.5684   $759.57   $759.60   $759.40