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 $57.39   9.643%   $62.9241   $62.92   $62.90   $62.90  
  Purchase #2 $57.78   12.498%   $65.0013   $65.00   $65.00   $65.00  
  Purchase #3 $167.26   10.260%   $184.4209   $184.42   $184.40   $184.40  
  Purchase #4 $96.46   8.194%   $104.3639   $104.36   $104.35   $104.40  
  Purchase #5 $57.97   9.111%   $63.2516   $63.25   $63.25   $63.30  
  Purchase #6 $70.36   3.580%   $72.8789   $72.88   $72.90   $72.90  
  Purchase #7 $180.77   4.606%   $189.0963   $189.10   $189.10   $189.10  
  7 purchase totals = $687.99       $741.9370   $741.93   $741.90   $742.00