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	$49.26	5.408%	$51.924	$51.92	$51.90	$51.90
Purchase #2	$223.61	9.236%	$244.2626	$244.26	$244.25	$244.30
Purchase #3	$99.54	12.133%	$111.6172	$111.62	$111.60	$111.60
Purchase #4	$207.25	9.818%	$227.5978	$227.60	$227.60	$227.60
Purchase #5	$6.43	12.311%	$7.2216	$7.22	$7.20	$7.20
Purchase #6	$116.37	13.318%	$131.8682	$131.87	$131.85	$131.90
Purchase #7	$88.83	8.813%	$96.6586	$96.66	$96.65	$96.70
7 purchase totals =	$791.29		$871.1500	$871.15	$871.05	$871.20