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 $222.35   8.486%   $241.2186   $241.22   $241.20   $241.20  
  Purchase #2 $107.74   10.355%   $118.8965   $118.90   $118.90   $118.90  
  Purchase #3 $220.83   13.214%   $250.0105   $250.01   $250.00   $250.00  
  Purchase #4 $233.87   4.746%   $244.9695   $244.97   $244.95   $245.00  
  Purchase #5 $8.55   13.330%   $9.6897   $9.69   $9.70   $9.70  
  Purchase #6 $95.74   6.134%   $101.6127   $101.61   $101.60   $101.60  
  Purchase #7 $91.88   5.423%   $96.8627   $96.86   $96.85   $96.90  
  7 purchase totals = $980.96       $1,063.2602   $1,063.26   $1,063.20   $1,063.30