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 $43.43   7.342%   $46.6186   $46.62   $46.60   $46.60  
  Purchase #2 $164.79   3.488%   $170.5379   $170.54   $170.55   $170.50  
  Purchase #3 $96.48   11.238%   $107.3224   $107.32   $107.30   $107.30  
  Purchase #4 $246.39   7.555%   $265.0048   $265.00   $265.00   $265.00  
  Purchase #5 $69.45   11.417%   $77.3791   $77.38   $77.40   $77.40  
  Purchase #6 $230.84   13.616%   $262.2712   $262.27   $262.25   $262.30  
  Purchase #7 $70.88   6.350%   $75.3809   $75.38   $75.40   $75.40  
  7 purchase totals = $922.26       $1,004.5149   $1,004.51   $1,004.50   $1,004.50