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	$31.37	13.260%	$35.5297	$35.53	$35.55	$35.50
Purchase #2	$164.83	7.332%	$176.9153	$176.92	$176.90	$176.90
Purchase #3	$60.40	6.624%	$64.4009	$64.40	$64.40	$64.40
Purchase #4	$70.86	11.273%	$78.848	$78.85	$78.85	$78.80
Purchase #5	$44.84	3.320%	$46.3287	$46.33	$46.35	$46.30
Purchase #6	$57.81	13.519%	$65.6253	$65.63	$65.65	$65.60
Purchase #7	$147.45	12.549%	$165.9535	$165.95	$165.95	$166.00
7 purchase totals =	$577.56		$633.6014	$633.61	$633.65	$633.50