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	$91.36	9.606%	$100.136	$100.14	$100.15	$100.10
Purchase #2	$119.28	12.748%	$134.4858	$134.49	$134.50	$134.50
Purchase #3	$244.65	12.276%	$274.6832	$274.68	$274.70	$274.70
Purchase #4	$149.75	11.796%	$167.4145	$167.41	$167.40	$167.40
Purchase #5	$199.68	11.596%	$222.8349	$222.83	$222.85	$222.80
Purchase #6	$125.65	13.108%	$142.1202	$142.12	$142.10	$142.10
Purchase #7	$65.40	7.368%	$70.2187	$70.22	$70.20	$70.20
7 purchase totals =	$995.77		$1,111.8933	$1,111.89	$1,111.90	$1,111.80