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 $244.96   3.697%   $254.0162   $254.02   $254.00   $254.00  
  Purchase #2 $16.31   11.785%   $18.2321   $18.23   $18.25   $18.20  
  Purchase #3 $104.95   3.179%   $108.2864   $108.29   $108.30   $108.30  
  Purchase #4 $94.29   5.381%   $99.3637   $99.36   $99.35   $99.40  
  Purchase #5 $200.77   8.332%   $217.4982   $217.50   $217.50   $217.50  
  Purchase #6 $245.47   3.417%   $253.8577   $253.86   $253.85   $253.90  
  Purchase #7 $97.53   11.602%   $108.8454   $108.85   $108.85   $108.80  
  7 purchase totals = $1,004.28       $1,060.0997   $1,060.11   $1,060.10   $1,060.10