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 $183.59   13.321%   $208.046   $208.05   $208.05   $208.00  
  Purchase #2 $117.54   5.543%   $124.0552   $124.06   $124.05   $124.10  
  Purchase #3 $122.67   13.229%   $138.898   $138.90   $138.90   $138.90  
  Purchase #4 $13.65   13.299%   $15.4653   $15.47   $15.45   $15.50  
  Purchase #5 $30.96   8.700%   $33.6535   $33.65   $33.65   $33.70  
  Purchase #6 $146.80   8.598%   $159.4219   $159.42   $159.40   $159.40  
  Purchase #7 $210.30   4.166%   $219.0611   $219.06   $219.05   $219.10  
  7 purchase totals = $825.51       $898.6010   $898.61   $898.55   $898.70