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 $231.60   11.118%   $257.3493   $257.35   $257.35   $257.30  
  Purchase #2 $152.90   7.683%   $164.6473   $164.65   $164.65   $164.60  
  Purchase #3 $192.86   6.849%   $206.069   $206.07   $206.05   $206.10  
  Purchase #4 $106.26   3.376%   $109.8473   $109.85   $109.85   $109.80  
  Purchase #5 $14.38   10.755%   $15.9266   $15.93   $15.95   $15.90  
  Purchase #6 $119.73   5.240%   $126.0039   $126.00   $126.00   $126.00  
  Purchase #7 $48.72   4.758%   $51.0381   $51.04   $51.05   $51.00  
  7 purchase totals = $866.45       $930.8815   $930.89   $930.90   $930.70