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 $119.92   12.153%   $134.4939   $134.49   $134.50   $134.50  
  Purchase #2 $239.29   11.393%   $266.5523   $266.55   $266.55   $266.60  
  Purchase #3 $147.46   3.714%   $152.9367   $152.94   $152.95   $152.90  
  Purchase #4 $53.34   5.274%   $56.1532   $56.15   $56.15   $56.20  
  Purchase #5 $233.64   4.641%   $244.4832   $244.48   $244.50   $244.50  
  Purchase #6 $167.90   8.141%   $181.5687   $181.57   $181.55   $181.60  
  Purchase #7 $185.95   9.415%   $203.4572   $203.46   $203.45   $203.50  
  7 purchase totals = $1,147.50       $1,239.6452   $1,239.64   $1,239.65   $1,239.80