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 $147.41   3.280%   $152.245   $152.25   $152.25   $152.20  
  Purchase #2 $235.73   10.357%   $260.1446   $260.14   $260.15   $260.10  
  Purchase #3 $17.84   4.781%   $18.6929   $18.69   $18.70   $18.70  
  Purchase #4 $34.68   9.161%   $37.857   $37.86   $37.85   $37.90  
  Purchase #5 $111.61   7.526%   $120.0098   $120.01   $120.00   $120.00  
  Purchase #6 $181.76   8.807%   $197.7676   $197.77   $197.75   $197.80  
  Purchase #7 $223.71   7.115%   $239.627   $239.63   $239.65   $239.60  
  7 purchase totals = $952.74       $1,026.3439   $1,026.35   $1,026.35   $1,026.30