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 $57.74   13.661%   $65.6279   $65.63   $65.65   $65.60  
  Purchase #2 $103.26   10.760%   $114.3708   $114.37   $114.35   $114.40  
  Purchase #3 $250.64   12.190%   $281.193   $281.19   $281.20   $281.20  
  Purchase #4 $91.63   12.509%   $103.092   $103.09   $103.10   $103.10  
  Purchase #5 $147.45   5.783%   $155.977   $155.98   $156.00   $156.00  
  Purchase #6 $148.48   13.506%   $168.5337   $168.53   $168.55   $168.50  
  Purchase #7 $25.97   4.211%   $27.0636   $27.06   $27.05   $27.10  
  7 purchase totals = $825.17       $915.8580   $915.85   $915.90   $915.90