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 $243.32   9.697%   $266.9147   $266.91   $266.90   $266.90  
  Purchase #2 $98.96   12.333%   $111.1647   $111.16   $111.15   $111.20  
  Purchase #3 $21.73   4.184%   $22.6392   $22.64   $22.65   $22.60  
  Purchase #4 $173.29   5.816%   $183.3685   $183.37   $183.35   $183.40  
  Purchase #5 $227.70   10.556%   $251.736   $251.74   $251.75   $251.70  
  Purchase #6 $159.51   13.277%   $180.6881   $180.69   $180.70   $180.70  
  Purchase #7 $153.46   4.255%   $159.9897   $159.99   $160.00   $160.00  
  7 purchase totals = $1,077.97       $1,176.5009   $1,176.50   $1,176.50   $1,176.50