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 $5.89   4.817%   $6.1737   $6.17   $6.15   $6.20  
  Purchase #2 $241.84   13.672%   $274.9044   $274.90   $274.90   $274.90  
  Purchase #3 $151.69   11.594%   $169.2769   $169.28   $169.30   $169.30  
  Purchase #4 $214.49   8.560%   $232.8503   $232.85   $232.85   $232.90  
  Purchase #5 $84.67   8.779%   $92.1032   $92.10   $92.10   $92.10  
  Purchase #6 $236.79   7.217%   $253.8791   $253.88   $253.90   $253.90  
  Purchase #7 $26.28   3.652%   $27.2397   $27.24   $27.25   $27.20  
  7 purchase totals = $961.65       $1,056.4273   $1,056.42   $1,056.45   $1,056.50