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 $68.52   13.299%   $77.6325   $77.63   $77.65   $77.60  
  Purchase #2 $218.71   9.366%   $239.1944   $239.19   $239.20   $239.20  
  Purchase #3 $208.28   8.357%   $225.686   $225.69   $225.70   $225.70  
  Purchase #4 $196.63   11.527%   $219.2955   $219.30   $219.30   $219.30  
  Purchase #5 $59.99   4.117%   $62.4598   $62.46   $62.45   $62.50  
  Purchase #6 $201.36   7.442%   $216.3452   $216.35   $216.35   $216.30  
  Purchase #7 $223.86   9.563%   $245.2677   $245.27   $245.25   $245.30  
  7 purchase totals = $1,177.35       $1,285.8811   $1,285.89   $1,285.90   $1,285.90