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	$159.77	9.817%	$175.4546	$175.45	$175.45	$175.50
Purchase #2	$225.86	13.309%	$255.9197	$255.92	$255.90	$255.90
Purchase #3	$244.73	10.250%	$269.8148	$269.81	$269.80	$269.80
Purchase #4	$56.74	3.172%	$58.5398	$58.54	$58.55	$58.50
Purchase #5	$242.54	13.737%	$275.8577	$275.86	$275.85	$275.90
Purchase #6	$134.39	7.318%	$144.2247	$144.22	$144.20	$144.20
Purchase #7	$98.61	10.185%	$108.6534	$108.65	$108.65	$108.70
7 purchase totals =	$1,162.64		$1,288.4647	$1,288.45	$1,288.40	$1,288.50