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 $118.53   4.448%   $123.8022   $123.80   $123.80   $123.80  
  Purchase #2 $55.62   8.392%   $60.2876   $60.29   $60.30   $60.30  
  Purchase #3 $232.85   11.207%   $258.9455   $258.95   $258.95   $258.90  
  Purchase #4 $76.70   5.134%   $80.6378   $80.64   $80.65   $80.60  
  Purchase #5 $93.55   10.743%   $103.6001   $103.60   $103.60   $103.60  
  Purchase #6 $105.49   9.311%   $115.3122   $115.31   $115.30   $115.30  
  Purchase #7 $35.28   9.827%   $38.747   $38.75   $38.75   $38.70  
  7 purchase totals = $718.02       $781.3324   $781.34   $781.35   $781.20