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 $239.27   9.782%   $262.6754   $262.68   $262.70   $262.70  
  Purchase #2 $206.64   8.781%   $224.7851   $224.79   $224.80   $224.80  
  Purchase #3 $102.36   6.636%   $109.1526   $109.15   $109.15   $109.20  
  Purchase #4 $175.88   13.614%   $199.8243   $199.82   $199.80   $199.80  
  Purchase #5 $59.89   11.783%   $66.9468   $66.95   $66.95   $66.90  
  Purchase #6 $43.54   7.132%   $46.6453   $46.65   $46.65   $46.60  
  Purchase #7 $227.67   6.802%   $243.1561   $243.16   $243.15   $243.20  
  7 purchase totals = $1,055.25       $1,153.1856   $1,153.20   $1,153.20   $1,153.20