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 $238.51   11.166%   $265.142   $265.14   $265.15   $265.10  
  Purchase #2 $209.92   10.608%   $232.1883   $232.19   $232.20   $232.20  
  Purchase #3 $112.65   11.489%   $125.5924   $125.59   $125.60   $125.60  
  Purchase #4 $178.90   6.532%   $190.5857   $190.59   $190.60   $190.60  
  Purchase #5 $84.48   4.203%   $88.0307   $88.03   $88.05   $88.00  
  Purchase #6 $211.40   5.193%   $222.378   $222.38   $222.40   $222.40  
  Purchase #7 $174.38   6.489%   $185.6955   $185.70   $185.70   $185.70  
  7 purchase totals = $1,210.24       $1,309.6126   $1,309.62   $1,309.70   $1,309.60