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 $182.65   8.447%   $198.0784   $198.08   $198.10   $198.10  
  Purchase #2 $24.77   13.846%   $28.1997   $28.20   $28.20   $28.20  
  Purchase #3 $176.26   11.478%   $196.4911   $196.49   $196.50   $196.50  
  Purchase #4 $132.93   6.149%   $141.1039   $141.10   $141.10   $141.10  
  Purchase #5 $85.93   12.543%   $96.7082   $96.71   $96.70   $96.70  
  Purchase #6 $183.27   6.489%   $195.1624   $195.16   $195.15   $195.20  
  Purchase #7 $45.42   6.240%   $48.2542   $48.25   $48.25   $48.30  
  7 purchase totals = $831.23       $903.9979   $903.99   $904.00   $904.10