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 $92.38   10.610%   $102.1815   $102.18   $102.20   $102.20  
  Purchase #2 $241.95   8.267%   $261.952   $261.95   $261.95   $262.00  
  Purchase #3 $224.73   5.206%   $236.4294   $236.43   $236.45   $236.40  
  Purchase #4 $247.48   8.550%   $268.6395   $268.64   $268.65   $268.60  
  Purchase #5 $109.80   9.645%   $120.3902   $120.39   $120.40   $120.40  
  Purchase #6 $50.75   12.194%   $56.9385   $56.94   $56.95   $56.90  
  Purchase #7 $248.39   11.715%   $277.4889   $277.49   $277.50   $277.50  
  7 purchase totals = $1,215.48       $1,324.0200   $1,324.02   $1,324.10   $1,324.00