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 $146.43   4.756%   $153.3942   $153.39   $153.40   $153.40  
  Purchase #2 $54.49   3.788%   $56.5541   $56.55   $56.55   $56.60  
  Purchase #3 $66.86   8.739%   $72.7029   $72.70   $72.70   $72.70  
  Purchase #4 $247.88   5.303%   $261.0251   $261.03   $261.05   $261.00  
  Purchase #5 $159.49   7.867%   $172.0371   $172.04   $172.05   $172.00  
  Purchase #6 $44.38   11.228%   $49.363   $49.36   $49.35   $49.40  
  Purchase #7 $63.25   5.723%   $66.8698   $66.87   $66.85   $66.90  
  7 purchase totals = $782.78       $831.9462   $831.94   $831.95   $832.00