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 $199.39   13.607%   $226.521   $226.52   $226.50   $226.50  
  Purchase #2 $226.34   6.397%   $240.819   $240.82   $240.80   $240.80  
  Purchase #3 $60.37   3.207%   $62.3061   $62.31   $62.30   $62.30  
  Purchase #4 $144.25   8.836%   $156.9959   $157.00   $157.00   $157.00  
  Purchase #5 $23.30   13.398%   $26.4217   $26.42   $26.40   $26.40  
  Purchase #6 $35.76   3.494%   $37.0095   $37.01   $37.00   $37.00  
  Purchase #7 $193.78   7.647%   $208.5984   $208.60   $208.60   $208.60  
  7 purchase totals = $883.19       $958.6716   $958.68   $958.60   $958.60