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 $219.51   6.799%   $234.4345   $234.43   $234.45   $234.40  
  Purchase #2 $149.91   3.836%   $155.6605   $155.66   $155.65   $155.70  
  Purchase #3 $237.36   13.226%   $268.7532   $268.75   $268.75   $268.80  
  Purchase #4 $242.26   12.391%   $272.2784   $272.28   $272.30   $272.30  
  Purchase #5 $222.36   4.858%   $233.1622   $233.16   $233.15   $233.20  
  Purchase #6 $177.27   3.719%   $183.8627   $183.86   $183.85   $183.90  
  Purchase #7 $52.71   3.276%   $54.4368   $54.44   $54.45   $54.40  
  7 purchase totals = $1,301.38       $1,402.5883   $1,402.58   $1,402.60   $1,402.70