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	$245.82	11.284%	$273.5583	$273.56	$273.55	$273.60
Purchase #2	$131.47	3.714%	$136.3528	$136.35	$136.35	$136.40
Purchase #3	$123.51	8.613%	$134.1479	$134.15	$134.15	$134.10
Purchase #4	$220.59	12.164%	$247.4226	$247.42	$247.40	$247.40
Purchase #5	$146.40	3.467%	$151.4757	$151.48	$151.50	$151.50
Purchase #6	$106.47	5.625%	$112.4589	$112.46	$112.45	$112.50
Purchase #7	$107.60	11.753%	$120.2462	$120.25	$120.25	$120.20
7 purchase totals =	$1,081.86		$1,175.6624	$1,175.67	$1,175.65	$1,175.70