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 $134.88   11.773%   $150.7594   $150.76   $150.75   $150.80  
  Purchase #2 $177.98   3.371%   $183.9797   $183.98   $184.00   $184.00  
  Purchase #3 $49.29   10.275%   $54.3545   $54.35   $54.35   $54.40  
  Purchase #4 $117.26   5.680%   $123.9204   $123.92   $123.90   $123.90  
  Purchase #5 $195.60   4.805%   $204.9986   $205.00   $205.00   $205.00  
  Purchase #6 $93.26   5.733%   $98.6066   $98.61   $98.60   $98.60  
  Purchase #7 $183.69   3.422%   $189.9759   $189.98   $190.00   $190.00  
  7 purchase totals = $951.96       $1,006.5951   $1,006.60   $1,006.60   $1,006.70