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 $234.54   9.844%   $257.6281   $257.63   $257.65   $257.60  
  Purchase #2 $22.42   10.472%   $24.7678   $24.77   $24.75   $24.80  
  Purchase #3 $68.73   13.634%   $78.1006   $78.10   $78.10   $78.10  
  Purchase #4 $168.26   4.768%   $176.2826   $176.28   $176.30   $176.30  
  Purchase #5 $152.83   5.209%   $160.7909   $160.79   $160.80   $160.80  
  Purchase #6 $211.81   7.603%   $227.9139   $227.91   $227.90   $227.90  
  Purchase #7 $121.34   13.777%   $138.057   $138.06   $138.05   $138.10  
  7 purchase totals = $979.93       $1,063.5409   $1,063.54   $1,063.55   $1,063.60