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	$19.40	10.871%	$21.509	$21.51	$21.50	$21.50
Purchase #2	$94.42	7.220%	$101.2371	$101.24	$101.25	$101.20
Purchase #3	$122.86	7.122%	$131.6101	$131.61	$131.60	$131.60
Purchase #4	$244.31	12.602%	$275.0979	$275.10	$275.10	$275.10
Purchase #5	$221.98	9.669%	$243.4432	$243.44	$243.45	$243.40
Purchase #6	$26.44	4.831%	$27.7173	$27.72	$27.70	$27.70
Purchase #7	$221.69	11.831%	$247.9181	$247.92	$247.90	$247.90
7 purchase totals =	$951.10		$1,048.5327	$1,048.54	$1,048.50	$1,048.40