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 $219.36   8.201%   $237.3497   $237.35   $237.35   $237.30  
  Purchase #2 $197.61   3.685%   $204.8919   $204.89   $204.90   $204.90  
  Purchase #3 $159.28   10.131%   $175.4167   $175.42   $175.40   $175.40  
  Purchase #4 $61.55   3.144%   $63.4851   $63.49   $63.50   $63.50  
  Purchase #5 $223.73   9.460%   $244.8949   $244.89   $244.90   $244.90  
  Purchase #6 $152.97   11.406%   $170.4178   $170.42   $170.40   $170.40  
  Purchase #7 $116.31   12.333%   $130.6545   $130.65   $130.65   $130.70  
  7 purchase totals = $1,130.81       $1,227.1106   $1,227.11   $1,227.10   $1,227.10