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	$72.82	11.733%	$81.364	$81.36	$81.35	$81.40
Purchase #2	$225.26	5.856%	$238.4512	$238.45	$238.45	$238.50
Purchase #3	$97.60	3.154%	$100.6783	$100.68	$100.70	$100.70
Purchase #4	$90.50	10.844%	$100.3138	$100.31	$100.30	$100.30
Purchase #5	$79.84	10.229%	$88.0068	$88.01	$88.00	$88.00
Purchase #6	$162.32	6.785%	$173.3334	$173.33	$173.35	$173.30
Purchase #7	$71.99	6.233%	$76.4771	$76.48	$76.50	$76.50
7 purchase totals =	$800.33		$858.6246	$858.62	$858.65	$858.70