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 $208.28   9.211%   $227.4647   $227.46   $227.45   $227.50  
  Purchase #2 $224.43   9.588%   $245.9483   $245.95   $245.95   $245.90  
  Purchase #3 $126.36   6.406%   $134.4546   $134.45   $134.45   $134.50  
  Purchase #4 $29.31   4.496%   $30.6278   $30.63   $30.65   $30.60  
  Purchase #5 $188.93   10.441%   $208.6562   $208.66   $208.65   $208.70  
  Purchase #6 $94.72   9.331%   $103.5583   $103.56   $103.55   $103.60  
  Purchase #7 $32.66   10.152%   $35.9756   $35.98   $36.00   $36.00  
  7 purchase totals = $904.69       $986.6855   $986.69   $986.70   $986.80