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 $169.86   7.151%   $182.0067   $182.01   $182.00   $182.00  
  Purchase #2 $158.91   11.236%   $176.7651   $176.77   $176.75   $176.80  
  Purchase #3 $131.91   4.172%   $137.4133   $137.41   $137.40   $137.40  
  Purchase #4 $183.54   4.203%   $191.2542   $191.25   $191.25   $191.30  
  Purchase #5 $98.62   8.639%   $107.1398   $107.14   $107.15   $107.10  
  Purchase #6 $69.98   8.592%   $75.9927   $75.99   $76.00   $76.00  
  Purchase #7 $125.47   13.490%   $142.3959   $142.40   $142.40   $142.40  
  7 purchase totals = $938.29       $1,012.9677   $1,012.97   $1,012.95   $1,013.00