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	$176.59	3.700%	$183.1238	$183.12	$183.10	$183.10
Purchase #2	$127.65	13.227%	$144.5343	$144.53	$144.55	$144.50
Purchase #3	$220.26	5.110%	$231.5153	$231.52	$231.50	$231.50
Purchase #4	$179.55	9.292%	$196.2338	$196.23	$196.25	$196.20
Purchase #5	$247.53	9.503%	$271.0528	$271.05	$271.05	$271.10
Purchase #6	$61.80	9.255%	$67.5196	$67.52	$67.50	$67.50
Purchase #7	$198.50	5.356%	$209.1317	$209.13	$209.15	$209.10
7 purchase totals =	$1,211.88		$1,303.1113	$1,303.10	$1,303.10	$1,303.00