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 $243.50   6.294%   $258.8259   $258.83   $258.85   $258.80  
  Purchase #2 $27.88   6.815%   $29.78   $29.78   $29.80   $29.80  
  Purchase #3 $67.94   8.767%   $73.8963   $73.90   $73.90   $73.90  
  Purchase #4 $231.67   12.810%   $261.3469   $261.35   $261.35   $261.30  
  Purchase #5 $176.88   13.139%   $200.1203   $200.12   $200.10   $200.10  
  Purchase #6 $245.46   5.163%   $258.1331   $258.13   $258.15   $258.10  
  Purchase #7 $195.30   12.783%   $220.2652   $220.27   $220.25   $220.30  
  7 purchase totals = $1,188.63       $1,302.3677   $1,302.38   $1,302.40   $1,302.30