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 $246.52   13.522%   $279.8544   $279.85   $279.85   $279.90  
  Purchase #2 $130.51   7.732%   $140.601   $140.60   $140.60   $140.60  
  Purchase #3 $42.27   9.591%   $46.3241   $46.32   $46.30   $46.30  
  Purchase #4 $188.31   11.612%   $210.1766   $210.18   $210.20   $210.20  
  Purchase #5 $66.81   4.371%   $69.7303   $69.73   $69.75   $69.70  
  Purchase #6 $209.84   12.693%   $236.475   $236.48   $236.50   $236.50  
  Purchase #7 $84.87   9.513%   $92.9437   $92.94   $92.95   $92.90  
  7 purchase totals = $969.13       $1,076.1051   $1,076.10   $1,076.15   $1,076.10