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 $59.77   9.290%   $65.3226   $65.32   $65.30   $65.30  
  Purchase #2 $162.54   11.215%   $180.7689   $180.77   $180.75   $180.80  
  Purchase #3 $175.61   9.514%   $192.3175   $192.32   $192.30   $192.30  
  Purchase #4 $17.49   10.772%   $19.374   $19.37   $19.35   $19.40  
  Purchase #5 $143.63   4.431%   $149.9942   $149.99   $150.00   $150.00  
  Purchase #6 $120.57   5.548%   $127.2592   $127.26   $127.25   $127.30  
  Purchase #7 $146.51   4.165%   $152.6121   $152.61   $152.60   $152.60  
  7 purchase totals = $826.12       $887.6485   $887.64   $887.55   $887.70