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 $241.26   13.633%   $274.151   $274.15   $274.15   $274.20  
  Purchase #2 $62.59   9.173%   $68.3314   $68.33   $68.35   $68.30  
  Purchase #3 $191.88   3.665%   $198.9124   $198.91   $198.90   $198.90  
  Purchase #4 $89.44   11.319%   $99.5637   $99.56   $99.55   $99.60  
  Purchase #5 $233.73   7.707%   $251.7436   $251.74   $251.75   $251.70  
  Purchase #6 $221.77   11.503%   $247.2802   $247.28   $247.30   $247.30  
  Purchase #7 $82.45   4.291%   $85.9879   $85.99   $86.00   $86.00  
  7 purchase totals = $1,123.12       $1,225.9702   $1,225.96   $1,226.00   $1,226.00