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	$75.57	4.243%	$78.7764	$78.78	$78.80	$78.80
Purchase #2	$200.79	11.245%	$223.3688	$223.37	$223.35	$223.40
Purchase #3	$123.74	4.166%	$128.895	$128.90	$128.90	$128.90
Purchase #4	$192.52	8.155%	$208.22	$208.22	$208.20	$208.20
Purchase #5	$109.93	7.150%	$117.79	$117.79	$117.80	$117.80
Purchase #6	$140.69	8.490%	$152.6346	$152.63	$152.65	$152.60
Purchase #7	$50.47	8.462%	$54.7408	$54.74	$54.75	$54.70
7 purchase totals =	$893.71		$964.4256	$964.43	$964.45	$964.40