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 $107.96   10.847%   $119.6704   $119.67   $119.65   $119.70  
  Purchase #2 $55.27   6.120%   $58.6525   $58.65   $58.65   $58.70  
  Purchase #3 $151.59   8.394%   $164.3145   $164.31   $164.30   $164.30  
  Purchase #4 $222.84   10.795%   $246.8956   $246.90   $246.90   $246.90  
  Purchase #5 $156.26   4.870%   $163.8699   $163.87   $163.85   $163.90  
  Purchase #6 $81.84   11.845%   $91.5339   $91.53   $91.55   $91.50  
  Purchase #7 $206.73   11.806%   $231.1365   $231.14   $231.15   $231.10  
  7 purchase totals = $982.49       $1,076.0733   $1,076.07   $1,076.05   $1,076.10