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 $178.54   12.871%   $201.5199   $201.52   $201.50   $201.50  
  Purchase #2 $206.65   5.241%   $217.4805   $217.48   $217.50   $217.50  
  Purchase #3 $205.63   5.636%   $217.2193   $217.22   $217.20   $217.20  
  Purchase #4 $57.52   11.853%   $64.3378   $64.34   $64.35   $64.30  
  Purchase #5 $141.27   7.374%   $151.6872   $151.69   $151.70   $151.70  
  Purchase #6 $139.69   12.376%   $156.978   $156.98   $157.00   $157.00  
  Purchase #7 $239.65   4.634%   $250.7554   $250.76   $250.75   $250.80  
  7 purchase totals = $1,168.95       $1,259.9781   $1,259.99   $1,260.00   $1,260.00