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 $28.83   12.534%   $32.4436   $32.44   $32.45   $32.40  
  Purchase #2 $157.73   6.704%   $168.3042   $168.30   $168.30   $168.30  
  Purchase #3 $210.99   4.442%   $220.3622   $220.36   $220.35   $220.40  
  Purchase #4 $196.44   7.235%   $210.6524   $210.65   $210.65   $210.70  
  Purchase #5 $226.31   4.397%   $236.2609   $236.26   $236.25   $236.30  
  Purchase #6 $20.50   7.439%   $22.025   $22.03   $22.05   $22.00  
  Purchase #7 $197.27   5.699%   $208.5124   $208.51   $208.50   $208.50  
  7 purchase totals = $1,038.07       $1,098.5607   $1,098.55   $1,098.55   $1,098.60