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 $248.31   7.205%   $266.2007   $266.20   $266.20   $266.20  
  Purchase #2 $122.37   3.561%   $126.7276   $126.73   $126.75   $126.70  
  Purchase #3 $88.69   8.532%   $96.257   $96.26   $96.25   $96.30  
  Purchase #4 $85.68   5.564%   $90.4472   $90.45   $90.45   $90.40  
  Purchase #5 $179.31   6.711%   $191.3435   $191.34   $191.35   $191.30  
  Purchase #6 $120.50   4.138%   $125.4863   $125.49   $125.50   $125.50  
  Purchase #7 $67.56   7.664%   $72.7378   $72.74   $72.75   $72.70  
  7 purchase totals = $912.42       $969.2001   $969.21   $969.25   $969.10