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 $98.65   5.714%   $104.2869   $104.29   $104.30   $104.30  
  Purchase #2 $112.87   6.767%   $120.5079   $120.51   $120.50   $120.50  
  Purchase #3 $179.26   8.118%   $193.8123   $193.81   $193.80   $193.80  
  Purchase #4 $213.90   12.222%   $240.0429   $240.04   $240.05   $240.00  
  Purchase #5 $166.46   7.173%   $178.4002   $178.40   $178.40   $178.40  
  Purchase #6 $58.66   12.542%   $66.0171   $66.02   $66.00   $66.00  
  Purchase #7 $26.64   13.599%   $30.2628   $30.26   $30.25   $30.30  
  7 purchase totals = $856.44       $933.3301   $933.33   $933.30   $933.30