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 $161.76   7.357%   $173.6607   $173.66   $173.65   $173.70  
  Purchase #2 $225.37   10.356%   $248.7093   $248.71   $248.70   $248.70  
  Purchase #3 $34.94   5.434%   $36.8386   $36.84   $36.85   $36.80  
  Purchase #4 $206.97   12.866%   $233.5988   $233.60   $233.60   $233.60  
  Purchase #5 $236.65   3.177%   $244.1684   $244.17   $244.15   $244.20  
  Purchase #6 $173.40   4.872%   $181.848   $181.85   $181.85   $181.80  
  Purchase #7 $106.25   12.800%   $119.85   $119.85   $119.85   $119.90  
  7 purchase totals = $1,145.34       $1,238.6738   $1,238.68   $1,238.65   $1,238.70