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 $245.55   8.435%   $266.2621   $266.26   $266.25   $266.30  
  Purchase #2 $174.44   7.688%   $187.8509   $187.85   $187.85   $187.90  
  Purchase #3 $168.45   8.214%   $182.2865   $182.29   $182.30   $182.30  
  Purchase #4 $182.42   4.854%   $191.2747   $191.27   $191.25   $191.30  
  Purchase #5 $87.66   8.650%   $95.2426   $95.24   $95.25   $95.20  
  Purchase #6 $208.78   7.383%   $224.1942   $224.19   $224.20   $224.20  
  Purchase #7 $143.91   8.537%   $156.1956   $156.20   $156.20   $156.20  
  7 purchase totals = $1,211.21       $1,303.3066   $1,303.30   $1,303.30   $1,303.40