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	$237.95	7.553%	$255.9224	$255.92	$255.90	$255.90
Purchase #2	$133.68	9.807%	$146.79	$146.79	$146.80	$146.80
Purchase #3	$45.75	10.629%	$50.6128	$50.61	$50.60	$50.60
Purchase #4	$204.30	9.519%	$223.7473	$223.75	$223.75	$223.70
Purchase #5	$98.32	6.374%	$104.5869	$104.59	$104.60	$104.60
Purchase #6	$10.55	10.281%	$11.6346	$11.63	$11.65	$11.60
Purchase #7	$133.83	10.571%	$147.9772	$147.98	$148.00	$148.00
7 purchase totals =	$864.38		$941.2712	$941.27	$941.30	$941.20