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 $114.39   10.598%   $126.5131   $126.51   $126.50   $126.50  
  Purchase #2 $127.64   4.126%   $132.9064   $132.91   $132.90   $132.90  
  Purchase #3 $202.74   4.246%   $211.3483   $211.35   $211.35   $211.30  
  Purchase #4 $171.37   11.253%   $190.6543   $190.65   $190.65   $190.70  
  Purchase #5 $76.27   9.536%   $83.5431   $83.54   $83.55   $83.50  
  Purchase #6 $62.50   4.402%   $65.2513   $65.25   $65.25   $65.30  
  Purchase #7 $204.73   11.160%   $227.5779   $227.58   $227.60   $227.60  
  7 purchase totals = $959.64       $1,037.7944   $1,037.79   $1,037.80   $1,037.80