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	$195.91	13.593%	$222.54	$222.54	$222.55	$222.50
Purchase #2	$34.88	9.653%	$38.247	$38.25	$38.25	$38.20
Purchase #3	$25.98	10.665%	$28.7508	$28.75	$28.75	$28.80
Purchase #4	$144.37	3.141%	$148.9047	$148.90	$148.90	$148.90
Purchase #5	$185.40	4.854%	$194.3993	$194.40	$194.40	$194.40
Purchase #6	$20.38	9.385%	$22.2927	$22.29	$22.30	$22.30
Purchase #7	$130.41	13.791%	$148.3948	$148.39	$148.40	$148.40
7 purchase totals =	$737.33		$803.5293	$803.52	$803.55	$803.50