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 $240.38   8.590%   $261.0286   $261.03   $261.05   $261.00  
  Purchase #2 $136.84   9.585%   $149.9561   $149.96   $149.95   $150.00  
  Purchase #3 $217.45   7.546%   $233.8588   $233.86   $233.85   $233.90  
  Purchase #4 $143.92   10.483%   $159.0071   $159.01   $159.00   $159.00  
  Purchase #5 $117.66   5.686%   $124.3501   $124.35   $124.35   $124.40  
  Purchase #6 $190.60   9.735%   $209.1549   $209.15   $209.15   $209.20  
  Purchase #7 $214.42   5.458%   $226.123   $226.12   $226.10   $226.10  
  7 purchase totals = $1,261.27       $1,363.4786   $1,363.48   $1,363.45   $1,363.60