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 $84.90   8.858%   $92.4204   $92.42   $92.40   $92.40  
  Purchase #2 $25.86   4.119%   $26.9252   $26.93   $26.95   $26.90  
  Purchase #3 $92.30   7.142%   $98.8921   $98.89   $98.90   $98.90  
  Purchase #4 $240.66   7.456%   $258.6036   $258.60   $258.60   $258.60  
  Purchase #5 $137.63   5.196%   $144.7813   $144.78   $144.80   $144.80  
  Purchase #6 $244.66   10.324%   $269.9187   $269.92   $269.90   $269.90  
  Purchase #7 $44.32   9.527%   $48.5424   $48.54   $48.55   $48.50  
  7 purchase totals = $870.33       $940.0837   $940.08   $940.10   $940.00