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 $240.39   8.657%   $261.2006   $261.20   $261.20   $261.20  
  Purchase #2 $249.85   8.673%   $271.5195   $271.52   $271.50   $271.50  
  Purchase #3 $154.60   6.262%   $164.2811   $164.28   $164.30   $164.30  
  Purchase #4 $26.88   7.825%   $28.9834   $28.98   $29.00   $29.00  
  Purchase #5 $98.79   6.699%   $105.4079   $105.41   $105.40   $105.40  
  Purchase #6 $7.54   7.851%   $8.132   $8.13   $8.15   $8.10  
  Purchase #7 $203.33   7.211%   $217.9921   $217.99   $218.00   $218.00  
  7 purchase totals = $981.38       $1,057.5166   $1,057.51   $1,057.55   $1,057.50