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 $57.31   9.559%   $62.7883   $62.79   $62.80   $62.80  
  Purchase #2 $176.97   7.448%   $190.1507   $190.15   $190.15   $190.20  
  Purchase #3 $150.88   7.761%   $162.5898   $162.59   $162.60   $162.60  
  Purchase #4 $151.46   9.836%   $166.3576   $166.36   $166.35   $166.40  
  Purchase #5 $222.63   6.807%   $237.7844   $237.78   $237.80   $237.80  
  Purchase #6 $147.56   9.471%   $161.5354   $161.54   $161.55   $161.50  
  Purchase #7 $115.61   3.735%   $119.928   $119.93   $119.95   $119.90  
  7 purchase totals = $1,022.42       $1,101.1342   $1,101.14   $1,101.20   $1,101.20