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 $154.91   10.859%   $171.7317   $171.73   $171.75   $171.70  
  Purchase #2 $21.74   4.353%   $22.6863   $22.69   $22.70   $22.70  
  Purchase #3 $177.54   8.648%   $192.8937   $192.89   $192.90   $192.90  
  Purchase #4 $189.85   3.842%   $197.144   $197.14   $197.15   $197.10  
  Purchase #5 $154.57   10.828%   $171.3068   $171.31   $171.30   $171.30  
  Purchase #6 $227.95   12.719%   $256.943   $256.94   $256.95   $256.90  
  Purchase #7 $111.94   6.311%   $119.0045   $119.00   $119.00   $119.00  
  7 purchase totals = $1,038.50       $1,131.7100   $1,131.70   $1,131.75   $1,131.60