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 $10.47   6.522%   $11.1529   $11.15   $11.15   $11.20  
  Purchase #2 $224.49   7.441%   $241.1943   $241.19   $241.20   $241.20  
  Purchase #3 $178.76   9.825%   $196.3232   $196.32   $196.30   $196.30  
  Purchase #4 $21.87   7.439%   $23.4969   $23.50   $23.50   $23.50  
  Purchase #5 $185.74   6.781%   $198.335   $198.34   $198.35   $198.30  
  Purchase #6 $219.33   3.225%   $226.4034   $226.40   $226.40   $226.40  
  Purchase #7 $91.32   9.869%   $100.3324   $100.33   $100.35   $100.30  
  7 purchase totals = $931.98       $997.2381   $997.23   $997.25   $997.20