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 $201.44   12.825%   $227.2747   $227.27   $227.25   $227.30  
  Purchase #2 $81.39   8.703%   $88.4734   $88.47   $88.45   $88.50  
  Purchase #3 $108.57   10.145%   $119.5844   $119.58   $119.60   $119.60  
  Purchase #4 $195.32   6.755%   $208.5139   $208.51   $208.50   $208.50  
  Purchase #5 $26.30   6.200%   $27.9306   $27.93   $27.95   $27.90  
  Purchase #6 $226.57   9.387%   $247.8381   $247.84   $247.85   $247.80  
  Purchase #7 $67.45   11.224%   $75.0206   $75.02   $75.00   $75.00  
  7 purchase totals = $907.04       $994.6357   $994.62   $994.60   $994.60