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 $234.42   12.594%   $263.9429   $263.94   $263.95   $263.90  
  Purchase #2 $38.83   6.141%   $41.2146   $41.21   $41.20   $41.20  
  Purchase #3 $190.81   7.748%   $205.594   $205.59   $205.60   $205.60  
  Purchase #4 $248.95   4.572%   $260.332   $260.33   $260.35   $260.30  
  Purchase #5 $96.73   10.750%   $107.1285   $107.13   $107.15   $107.10  
  Purchase #6 $120.65   4.795%   $126.4352   $126.44   $126.45   $126.40  
  Purchase #7 $189.38   4.167%   $197.2715   $197.27   $197.25   $197.30  
  7 purchase totals = $1,119.77       $1,201.9187   $1,201.91   $1,201.95   $1,201.80