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 $88.55   6.781%   $94.5546   $94.55   $94.55   $94.60  
  Purchase #2 $234.41   4.558%   $245.0944   $245.09   $245.10   $245.10  
  Purchase #3 $27.54   8.681%   $29.9307   $29.93   $29.95   $29.90  
  Purchase #4 $65.47   6.768%   $69.901   $69.90   $69.90   $69.90  
  Purchase #5 $179.43   3.567%   $185.8303   $185.83   $185.85   $185.80  
  Purchase #6 $233.98   3.634%   $242.4828   $242.48   $242.50   $242.50  
  Purchase #7 $34.33   6.234%   $36.4701   $36.47   $36.45   $36.50  
  7 purchase totals = $863.71       $904.2639   $904.25   $904.30   $904.30