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	$154.47	8.240%	$167.1983	$167.20	$167.20	$167.20
Purchase #2	$73.31	13.780%	$83.4121	$83.41	$83.40	$83.40
Purchase #3	$153.81	12.264%	$172.6733	$172.67	$172.65	$172.70
Purchase #4	$69.91	12.769%	$78.8368	$78.84	$78.85	$78.80
Purchase #5	$78.45	3.634%	$81.3009	$81.30	$81.30	$81.30
Purchase #6	$136.82	9.391%	$149.6688	$149.67	$149.65	$149.70
Purchase #7	$245.37	7.650%	$264.1408	$264.14	$264.15	$264.10
7 purchase totals =	$912.14		$997.2310	$997.23	$997.20	$997.20