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	$142.32	12.163%	$159.6304	$159.63	$159.65	$159.60
Purchase #2	$89.98	10.351%	$99.2938	$99.29	$99.30	$99.30
Purchase #3	$185.33	8.349%	$200.8032	$200.80	$200.80	$200.80
Purchase #4	$124.57	4.569%	$130.2616	$130.26	$130.25	$130.30
Purchase #5	$211.29	13.740%	$240.3212	$240.32	$240.30	$240.30
Purchase #6	$129.79	11.612%	$144.8612	$144.86	$144.85	$144.90
Purchase #7	$48.62	6.719%	$51.8868	$51.89	$51.90	$51.90
7 purchase totals =	$931.90		$1,027.0582	$1,027.05	$1,027.05	$1,027.10