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 $208.54   13.768%   $237.2518   $237.25   $237.25   $237.30  
  Purchase #2 $245.48   4.673%   $256.9513   $256.95   $256.95   $257.00  
  Purchase #3 $46.97   4.544%   $49.1043   $49.10   $49.10   $49.10  
  Purchase #4 $7.59   8.149%   $8.2085   $8.21   $8.20   $8.20  
  Purchase #5 $237.73   11.403%   $264.8384   $264.84   $264.85   $264.80  
  Purchase #6 $42.43   10.657%   $46.9518   $46.95   $46.95   $47.00  
  Purchase #7 $131.45   12.661%   $148.0929   $148.09   $148.10   $148.10  
  7 purchase totals = $920.19       $1,011.3990   $1,011.39   $1,011.40   $1,011.50