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	$87.52	4.758%	$91.6842	$91.68	$91.70	$91.70
Purchase #2	$151.25	9.749%	$165.9954	$166.00	$166.00	$166.00
Purchase #3	$222.33	9.549%	$243.5603	$243.56	$243.55	$243.60
Purchase #4	$176.83	9.404%	$193.4591	$193.46	$193.45	$193.50
Purchase #5	$189.84	3.295%	$196.0952	$196.10	$196.10	$196.10
Purchase #6	$185.69	5.599%	$196.0868	$196.09	$196.10	$196.10
Purchase #7	$210.76	8.864%	$229.4418	$229.44	$229.45	$229.40
7 purchase totals =	$1,224.22		$1,316.3228	$1,316.33	$1,316.35	$1,316.40