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 $61.42   9.544%   $67.2819   $67.28   $67.30   $67.30  
  Purchase #2 $223.96   8.462%   $242.9115   $242.91   $242.90   $242.90  
  Purchase #3 $143.47   13.463%   $162.7854   $162.79   $162.80   $162.80  
  Purchase #4 $147.53   11.327%   $164.2407   $164.24   $164.25   $164.20  
  Purchase #5 $234.90   4.362%   $245.1463   $245.15   $245.15   $245.10  
  Purchase #6 $98.95   3.387%   $102.3014   $102.30   $102.30   $102.30  
  Purchase #7 $57.86   7.222%   $62.0386   $62.04   $62.05   $62.00  
  7 purchase totals = $968.09       $1,046.7058   $1,046.71   $1,046.75   $1,046.60