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 $151.27   10.241%   $166.7616   $166.76   $166.75   $166.80  
  Purchase #2 $139.57   6.325%   $148.3978   $148.40   $148.40   $148.40  
  Purchase #3 $130.49   10.460%   $144.1393   $144.14   $144.15   $144.10  
  Purchase #4 $223.57   11.102%   $248.3907   $248.39   $248.40   $248.40  
  Purchase #5 $162.76   4.844%   $170.6441   $170.64   $170.65   $170.60  
  Purchase #6 $7.44   10.297%   $8.2061   $8.21   $8.20   $8.20  
  Purchase #7 $223.47   4.289%   $233.0546   $233.05   $233.05   $233.10  
  7 purchase totals = $1,038.57       $1,119.5942   $1,119.59   $1,119.60   $1,119.60