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 $196.91   4.243%   $205.2649   $205.26   $205.25   $205.30  
  Purchase #2 $132.86   8.273%   $143.8515   $143.85   $143.85   $143.90  
  Purchase #3 $50.34   12.453%   $56.6088   $56.61   $56.60   $56.60  
  Purchase #4 $62.65   9.466%   $68.5804   $68.58   $68.60   $68.60  
  Purchase #5 $150.34   3.680%   $155.8725   $155.87   $155.85   $155.90  
  Purchase #6 $175.44   5.527%   $185.1366   $185.14   $185.15   $185.10  
  Purchase #7 $206.53   5.453%   $217.7921   $217.79   $217.80   $217.80  
  7 purchase totals = $975.07       $1,033.1068   $1,033.10   $1,033.10   $1,033.20