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 $250.56   4.136%   $260.9232   $260.92   $260.90   $260.90  
  Purchase #2 $66.69   9.732%   $73.1803   $73.18   $73.20   $73.20  
  Purchase #3 $116.29   3.716%   $120.6113   $120.61   $120.60   $120.60  
  Purchase #4 $211.77   4.627%   $221.5686   $221.57   $221.55   $221.60  
  Purchase #5 $146.63   10.294%   $161.7241   $161.72   $161.70   $161.70  
  Purchase #6 $108.55   11.628%   $121.1722   $121.17   $121.15   $121.20  
  Purchase #7 $67.39   10.285%   $74.3211   $74.32   $74.30   $74.30  
  7 purchase totals = $967.88       $1,033.5008   $1,033.49   $1,033.40   $1,033.50