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 $249.60   9.872%   $274.2405   $274.24   $274.25   $274.20  
  Purchase #2 $14.69   11.154%   $16.3285   $16.33   $16.35   $16.30  
  Purchase #3 $169.36   4.386%   $176.7881   $176.79   $176.80   $176.80  
  Purchase #4 $210.33   7.279%   $225.6399   $225.64   $225.65   $225.60  
  Purchase #5 $187.35   6.515%   $199.5559   $199.56   $199.55   $199.60  
  Purchase #6 $241.51   8.483%   $261.9973   $262.00   $262.00   $262.00  
  Purchase #7 $169.91   7.268%   $182.2591   $182.26   $182.25   $182.30  
  7 purchase totals = $1,242.75       $1,336.8093   $1,336.82   $1,336.85   $1,336.80