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 $204.84   8.707%   $222.6754   $222.68   $222.70   $222.70  
  Purchase #2 $63.44   13.150%   $71.7824   $71.78   $71.80   $71.80  
  Purchase #3 $35.62   5.568%   $37.6033   $37.60   $37.60   $37.60  
  Purchase #4 $86.58   11.724%   $96.7306   $96.73   $96.75   $96.70  
  Purchase #5 $183.26   8.262%   $198.4009   $198.40   $198.40   $198.40  
  Purchase #6 $159.30   11.326%   $177.3423   $177.34   $177.35   $177.30  
  Purchase #7 $240.37   10.542%   $265.7098   $265.71   $265.70   $265.70  
  7 purchase totals = $973.41       $1,070.2447   $1,070.24   $1,070.30   $1,070.20