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 $242.93   9.514%   $266.0424   $266.04   $266.05   $266.00  
  Purchase #2 $203.87   10.235%   $224.7361   $224.74   $224.75   $224.70  
  Purchase #3 $241.88   3.655%   $250.7207   $250.72   $250.70   $250.70  
  Purchase #4 $220.77   13.747%   $251.1193   $251.12   $251.10   $251.10  
  Purchase #5 $29.76   12.589%   $33.5065   $33.51   $33.50   $33.50  
  Purchase #6 $175.80   6.560%   $187.3325   $187.33   $187.35   $187.30  
  Purchase #7 $232.58   9.138%   $253.8332   $253.83   $253.85   $253.80  
  7 purchase totals = $1,347.59       $1,467.2907   $1,467.29   $1,467.30   $1,467.10