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	$62.43	3.308%	$64.4952	$64.50	$64.50	$64.50
Purchase #2	$122.59	11.403%	$136.5689	$136.57	$136.55	$136.60
Purchase #3	$169.73	3.468%	$175.6162	$175.62	$175.60	$175.60
Purchase #4	$130.73	10.388%	$144.3102	$144.31	$144.30	$144.30
Purchase #5	$7.84	10.820%	$8.6883	$8.69	$8.70	$8.70
Purchase #6	$145.57	4.705%	$152.4191	$152.42	$152.40	$152.40
Purchase #7	$75.42	10.846%	$83.6001	$83.60	$83.60	$83.60
7 purchase totals =	$714.31		$765.6980	$765.71	$765.65	$765.70