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 $30.71   9.300%   $33.566   $33.57   $33.55   $33.60  
  Purchase #2 $91.62   4.355%   $95.6101   $95.61   $95.60   $95.60  
  Purchase #3 $200.94   5.484%   $211.9595   $211.96   $211.95   $212.00  
  Purchase #4 $59.43   10.183%   $65.4818   $65.48   $65.50   $65.50  
  Purchase #5 $86.36   10.175%   $95.1471   $95.15   $95.15   $95.10  
  Purchase #6 $161.28   10.266%   $177.837   $177.84   $177.85   $177.80  
  Purchase #7 $110.96   3.266%   $114.584   $114.58   $114.60   $114.60  
  7 purchase totals = $741.30       $794.1855   $794.19   $794.20   $794.20