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	$155.79	6.819%	$166.4133	$166.41	$166.40	$166.40
Purchase #2	$116.38	9.593%	$127.5443	$127.54	$127.55	$127.50
Purchase #3	$242.33	7.385%	$260.2261	$260.23	$260.25	$260.20
Purchase #4	$217.90	6.189%	$231.3858	$231.39	$231.40	$231.40
Purchase #5	$57.75	5.827%	$61.1151	$61.12	$61.10	$61.10
Purchase #6	$65.48	3.198%	$67.5741	$67.57	$67.55	$67.60
Purchase #7	$68.99	3.595%	$71.4702	$71.47	$71.45	$71.50
7 purchase totals =	$924.62		$985.7289	$985.73	$985.70	$985.70