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 $216.73   6.534%   $230.8911   $230.89   $230.90   $230.90  
  Purchase #2 $163.57   10.856%   $181.3272   $181.33   $181.35   $181.30  
  Purchase #3 $231.29   3.438%   $239.2418   $239.24   $239.25   $239.20  
  Purchase #4 $205.96   10.473%   $227.5302   $227.53   $227.55   $227.50  
  Purchase #5 $21.28   11.391%   $23.704   $23.70   $23.70   $23.70  
  Purchase #6 $166.81   10.206%   $183.8346   $183.83   $183.85   $183.80  
  Purchase #7 $35.50   12.423%   $39.9102   $39.91   $39.90   $39.90  
  7 purchase totals = $1,041.14       $1,126.4391   $1,126.43   $1,126.50   $1,126.30