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 $60.60   4.466%   $63.3064   $63.31   $63.30   $63.30  
  Purchase #2 $196.42   10.749%   $217.5332   $217.53   $217.55   $217.50  
  Purchase #3 $223.84   5.868%   $236.9749   $236.97   $236.95   $237.00  
  Purchase #4 $62.57   13.366%   $70.9331   $70.93   $70.95   $70.90  
  Purchase #5 $121.77   4.150%   $126.8235   $126.82   $126.80   $126.80  
  Purchase #6 $216.72   6.117%   $229.9768   $229.98   $230.00   $230.00  
  Purchase #7 $79.82   3.773%   $82.8316   $82.83   $82.85   $82.80  
  7 purchase totals = $961.74       $1,028.3795   $1,028.37   $1,028.40   $1,028.30