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 $111.82   12.692%   $126.0122   $126.01   $126.00   $126.00  
  Purchase #2 $59.83   11.356%   $66.6243   $66.62   $66.60   $66.60  
  Purchase #3 $107.48   10.567%   $118.8374   $118.84   $118.85   $118.80  
  Purchase #4 $71.72   11.773%   $80.1636   $80.16   $80.15   $80.20  
  Purchase #5 $249.54   10.589%   $275.9638   $275.96   $275.95   $276.00  
  Purchase #6 $32.94   10.757%   $36.4834   $36.48   $36.50   $36.50  
  Purchase #7 $75.67   7.781%   $81.5579   $81.56   $81.55   $81.60  
  7 purchase totals = $709.00       $785.6426   $785.63   $785.60   $785.70