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 $32.86   4.488%   $34.3348   $34.33   $34.35   $34.30  
  Purchase #2 $186.27   7.107%   $199.5082   $199.51   $199.50   $199.50  
  Purchase #3 $95.28   3.707%   $98.812   $98.81   $98.80   $98.80  
  Purchase #4 $194.87   6.716%   $207.9575   $207.96   $207.95   $208.00  
  Purchase #5 $208.62   5.487%   $220.067   $220.07   $220.05   $220.10  
  Purchase #6 $30.42   6.746%   $32.4721   $32.47   $32.45   $32.50  
  Purchase #7 $177.48   3.665%   $183.9846   $183.98   $184.00   $184.00  
  7 purchase totals = $925.80       $977.1362   $977.13   $977.10   $977.20