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 $164.70   6.233%   $174.9658   $174.97   $174.95   $175.00  
  Purchase #2 $228.60   3.436%   $236.4547   $236.45   $236.45   $236.50  
  Purchase #3 $9.53   7.358%   $10.2312   $10.23   $10.25   $10.20  
  Purchase #4 $59.26   9.574%   $64.9336   $64.93   $64.95   $64.90  
  Purchase #5 $205.51   4.831%   $215.4382   $215.44   $215.45   $215.40  
  Purchase #6 $154.25   13.417%   $174.9457   $174.95   $174.95   $174.90  
  Purchase #7 $58.55   6.517%   $62.3657   $62.37   $62.35   $62.40  
  7 purchase totals = $880.40       $939.3349   $939.34   $939.35   $939.30