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 $55.79   8.868%   $60.7375   $60.74   $60.75   $60.70  
  Purchase #2 $143.79   12.856%   $162.2756   $162.28   $162.30   $162.30  
  Purchase #3 $59.76   9.175%   $65.243   $65.24   $65.25   $65.20  
  Purchase #4 $85.67   9.860%   $94.1171   $94.12   $94.10   $94.10  
  Purchase #5 $35.49   6.103%   $37.656   $37.66   $37.65   $37.70  
  Purchase #6 $68.76   8.162%   $74.3722   $74.37   $74.35   $74.40  
  Purchase #7 $99.50   8.692%   $108.1485   $108.15   $108.15   $108.10  
  7 purchase totals = $548.76       $602.5499   $602.56   $602.55   $602.50