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 $88.94   10.631%   $98.3952   $98.40   $98.40   $98.40  
  Purchase #2 $15.71   3.145%   $16.2041   $16.20   $16.20   $16.20  
  Purchase #3 $51.64   7.723%   $55.6282   $55.63   $55.65   $55.60  
  Purchase #4 $11.69   6.179%   $12.4123   $12.41   $12.40   $12.40  
  Purchase #5 $8.83   10.346%   $9.7436   $9.74   $9.75   $9.70  
  Purchase #6 $43.50   10.185%   $47.9305   $47.93   $47.95   $47.90  
  Purchase #7 $113.68   10.836%   $125.9984   $126.00   $126.00   $126.00  
  7 purchase totals = $333.99       $366.3123   $366.31   $366.35   $366.20