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 $170.53   7.485%   $183.2942   $183.29   $183.30   $183.30  
  Purchase #2 $164.28   13.636%   $186.6812   $186.68   $186.70   $186.70  
  Purchase #3 $27.37   11.761%   $30.589   $30.59   $30.60   $30.60  
  Purchase #4 $40.79   6.127%   $43.2892   $43.29   $43.30   $43.30  
  Purchase #5 $218.46   11.746%   $244.1203   $244.12   $244.10   $244.10  
  Purchase #6 $242.36   4.640%   $253.6055   $253.61   $253.60   $253.60  
  Purchase #7 $12.38   10.347%   $13.661   $13.66   $13.65   $13.70  
  7 purchase totals = $876.17       $955.2404   $955.24   $955.25   $955.30