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 $190.53   10.283%   $210.1222   $210.12   $210.10   $210.10  
  Purchase #2 $82.86   13.629%   $94.153   $94.15   $94.15   $94.20  
  Purchase #3 $19.68   5.842%   $20.8297   $20.83   $20.85   $20.80  
  Purchase #4 $41.81   3.756%   $43.3804   $43.38   $43.40   $43.40  
  Purchase #5 $107.47   10.378%   $118.6232   $118.62   $118.60   $118.60  
  Purchase #6 $206.51   6.305%   $219.5305   $219.53   $219.55   $219.50  
  Purchase #7 $232.29   6.765%   $248.0044   $248.00   $248.00   $248.00  
  7 purchase totals = $881.15       $954.6434   $954.63   $954.65   $954.60