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	$236.95	11.123%	$263.3059	$263.31	$263.30	$263.30
Purchase #2	$99.90	8.523%	$108.4145	$108.41	$108.40	$108.40
Purchase #3	$39.26	5.434%	$41.3934	$41.39	$41.40	$41.40
Purchase #4	$133.79	10.214%	$147.4553	$147.46	$147.45	$147.50
Purchase #5	$247.80	7.178%	$265.5871	$265.59	$265.60	$265.60
Purchase #6	$148.93	5.753%	$157.4979	$157.50	$157.50	$157.50
Purchase #7	$53.72	3.300%	$55.4928	$55.49	$55.50	$55.50
7 purchase totals =	$960.35		$1,039.1469	$1,039.15	$1,039.15	$1,039.20