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 $175.27   13.846%   $199.5379   $199.54   $199.55   $199.50  
  Purchase #2 $54.86   13.580%   $62.31   $62.31   $62.30   $62.30  
  Purchase #3 $103.65   3.867%   $107.6581   $107.66   $107.65   $107.70  
  Purchase #4 $116.53   11.727%   $130.1955   $130.20   $130.20   $130.20  
  Purchase #5 $88.42   4.387%   $92.299   $92.30   $92.30   $92.30  
  Purchase #6 $156.45   12.647%   $176.2362   $176.24   $176.25   $176.20  
  Purchase #7 $212.39   10.388%   $234.4531   $234.45   $234.45   $234.50  
  7 purchase totals = $907.57       $1,002.6898   $1,002.70   $1,002.70   $1,002.70