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	$48.28	4.274%	$50.3435	$50.34	$50.35	$50.30
Purchase #2	$209.82	12.190%	$235.3971	$235.40	$235.40	$235.40
Purchase #3	$129.50	3.840%	$134.4728	$134.47	$134.45	$134.50
Purchase #4	$106.89	12.613%	$120.372	$120.37	$120.35	$120.40
Purchase #5	$134.25	13.445%	$152.2999	$152.30	$152.30	$152.30
Purchase #6	$107.32	4.194%	$111.821	$111.82	$111.80	$111.80
Purchase #7	$128.90	4.205%	$134.3202	$134.32	$134.30	$134.30
7 purchase totals =	$864.96		$939.0265	$939.02	$938.95	$939.00