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 $61.54   8.118%   $66.5358   $66.54   $66.55   $66.50  
  Purchase #2 $134.55   13.452%   $152.6497   $152.65   $152.65   $152.60  
  Purchase #3 $107.65   4.226%   $112.1993   $112.20   $112.20   $112.20  
  Purchase #4 $72.88   5.632%   $76.9846   $76.98   $77.00   $77.00  
  Purchase #5 $26.48   5.738%   $27.9994   $28.00   $28.00   $28.00  
  Purchase #6 $119.88   11.180%   $133.2826   $133.28   $133.30   $133.30  
  Purchase #7 $214.44   13.593%   $243.5888   $243.59   $243.60   $243.60  
  7 purchase totals = $737.42       $813.2402   $813.24   $813.30   $813.20