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 $65.66   3.206%   $67.7651   $67.77   $67.75   $67.80  
  Purchase #2 $216.93   9.247%   $236.9895   $236.99   $237.00   $237.00  
  Purchase #3 $227.59   13.367%   $258.012   $258.01   $258.00   $258.00  
  Purchase #4 $123.76   8.839%   $134.6991   $134.70   $134.70   $134.70  
  Purchase #5 $244.61   5.154%   $257.2172   $257.22   $257.20   $257.20  
  Purchase #6 $9.63   7.458%   $10.3482   $10.35   $10.35   $10.30  
  Purchase #7 $76.74   11.199%   $85.3341   $85.33   $85.35   $85.30  
  7 purchase totals = $964.92       $1,050.3652   $1,050.37   $1,050.35   $1,050.30