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 $113.48   9.133%   $123.8441   $123.84   $123.85   $123.80  
  Purchase #2 $94.54   9.240%   $103.2755   $103.28   $103.30   $103.30  
  Purchase #3 $186.77   10.590%   $206.5489   $206.55   $206.55   $206.50  
  Purchase #4 $158.51   11.574%   $176.8559   $176.86   $176.85   $176.90  
  Purchase #5 $175.62   12.730%   $197.9764   $197.98   $198.00   $198.00  
  Purchase #6 $115.72   8.528%   $125.5886   $125.59   $125.60   $125.60  
  Purchase #7 $132.79   7.511%   $142.7639   $142.76   $142.75   $142.80  
  7 purchase totals = $977.43       $1,076.8533   $1,076.86   $1,076.90   $1,076.90