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 $240.80   8.294%   $260.772   $260.77   $260.75   $260.80  
  Purchase #2 $201.46   12.698%   $227.0414   $227.04   $227.05   $227.00  
  Purchase #3 $134.42   3.757%   $139.4702   $139.47   $139.45   $139.50  
  Purchase #4 $178.52   3.603%   $184.9521   $184.95   $184.95   $185.00  
  Purchase #5 $246.41   7.543%   $264.9967   $265.00   $265.00   $265.00  
  Purchase #6 $22.37   8.178%   $24.1994   $24.20   $24.20   $24.20  
  Purchase #7 $186.86   3.606%   $193.5982   $193.60   $193.60   $193.60  
  7 purchase totals = $1,210.84       $1,295.0300   $1,295.03   $1,295.00   $1,295.10