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 $181.41   6.221%   $192.6955   $192.70   $192.70   $192.70  
  Purchase #2 $221.46   11.535%   $247.0054   $247.01   $247.00   $247.00  
  Purchase #3 $112.34   9.848%   $123.4032   $123.40   $123.40   $123.40  
  Purchase #4 $84.73   13.299%   $95.9982   $96.00   $96.00   $96.00  
  Purchase #5 $165.36   13.268%   $187.3   $187.30   $187.30   $187.30  
  Purchase #6 $198.82   7.637%   $214.0039   $214.00   $214.00   $214.00  
  Purchase #7 $233.38   12.774%   $263.192   $263.19   $263.20   $263.20  
  7 purchase totals = $1,197.50       $1,323.5982   $1,323.60   $1,323.60   $1,323.60