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 $248.87   10.301%   $274.5061   $274.51   $274.50   $274.50  
  Purchase #2 $45.43   5.660%   $48.0013   $48.00   $48.00   $48.00  
  Purchase #3 $49.36   5.149%   $51.9015   $51.90   $51.90   $51.90  
  Purchase #4 $159.86   4.624%   $167.2519   $167.25   $167.25   $167.30  
  Purchase #5 $91.29   13.548%   $103.658   $103.66   $103.65   $103.70  
  Purchase #6 $60.82   7.408%   $65.3255   $65.33   $65.35   $65.30  
  Purchase #7 $192.42   12.864%   $217.1729   $217.17   $217.15   $217.20  
  7 purchase totals = $848.05       $927.8172   $927.82   $927.80   $927.90