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 $243.74   7.293%   $261.516   $261.52   $261.50   $261.50  
  Purchase #2 $44.50   5.172%   $46.8015   $46.80   $46.80   $46.80  
  Purchase #3 $60.71   10.755%   $67.2394   $67.24   $67.25   $67.20  
  Purchase #4 $55.38   12.162%   $62.1153   $62.12   $62.10   $62.10  
  Purchase #5 $96.95   9.376%   $106.04   $106.04   $106.05   $106.00  
  Purchase #6 $67.37   11.744%   $75.2819   $75.28   $75.30   $75.30  
  Purchase #7 $230.48   8.698%   $250.5272   $250.53   $250.55   $250.50  
  7 purchase totals = $799.13       $869.5213   $869.53   $869.55   $869.40