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 $76.34   8.294%   $82.6716   $82.67   $82.65   $82.70  
  Purchase #2 $190.28   6.344%   $202.3514   $202.35   $202.35   $202.40  
  Purchase #3 $21.27   8.339%   $23.0437   $23.04   $23.05   $23.00  
  Purchase #4 $184.36   4.861%   $193.3217   $193.32   $193.30   $193.30  
  Purchase #5 $62.69   6.446%   $66.731   $66.73   $66.75   $66.70  
  Purchase #6 $164.87   3.544%   $170.713   $170.71   $170.70   $170.70  
  Purchase #7 $194.25   6.119%   $206.1362   $206.14   $206.15   $206.10  
  7 purchase totals = $894.06       $944.9686   $944.96   $944.95   $944.90