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	$51.74	11.140%	$57.5038	$57.50	$57.50	$57.50
Purchase #2	$89.53	4.549%	$93.6027	$93.60	$93.60	$93.60
Purchase #3	$204.58	8.212%	$221.3801	$221.38	$221.40	$221.40
Purchase #4	$250.62	4.399%	$261.6448	$261.64	$261.65	$261.60
Purchase #5	$57.42	3.715%	$59.5532	$59.55	$59.55	$59.60
Purchase #6	$128.97	4.327%	$134.5505	$134.55	$134.55	$134.60
Purchase #7	$233.39	9.741%	$256.1245	$256.12	$256.10	$256.10
7 purchase totals =	$1,016.25		$1,084.3596	$1,084.34	$1,084.35	$1,084.40