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 $228.25   4.854%   $239.3293   $239.33   $239.35   $239.30  
  Purchase #2 $234.66   13.360%   $266.0106   $266.01   $266.00   $266.00  
  Purchase #3 $18.86   11.138%   $20.9606   $20.96   $20.95   $21.00  
  Purchase #4 $109.87   3.531%   $113.7495   $113.75   $113.75   $113.70  
  Purchase #5 $95.60   9.437%   $104.6218   $104.62   $104.60   $104.60  
  Purchase #6 $80.64   6.302%   $85.7219   $85.72   $85.70   $85.70  
  Purchase #7 $103.92   13.299%   $117.7403   $117.74   $117.75   $117.70  
  7 purchase totals = $871.80       $948.1340   $948.13   $948.10   $948.00