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 $234.62   11.745%   $262.1761   $262.18   $262.20   $262.20  
  Purchase #2 $174.86   4.557%   $182.8284   $182.83   $182.85   $182.80  
  Purchase #3 $207.30   8.685%   $225.304   $225.30   $225.30   $225.30  
  Purchase #4 $69.99   7.825%   $75.4667   $75.47   $75.45   $75.50  
  Purchase #5 $100.63   10.161%   $110.855   $110.86   $110.85   $110.90  
  Purchase #6 $214.36   6.830%   $229.0008   $229.00   $229.00   $229.00  
  Purchase #7 $82.80   5.566%   $87.4086   $87.41   $87.40   $87.40  
  7 purchase totals = $1,084.56       $1,173.0396   $1,173.05   $1,173.05   $1,173.10