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	$151.84	11.104%	$168.7003	$168.70	$168.70	$168.70
Purchase #2	$128.60	10.801%	$142.4901	$142.49	$142.50	$142.50
Purchase #3	$159.83	3.586%	$165.5615	$165.56	$165.55	$165.60
Purchase #4	$181.44	3.847%	$188.42	$188.42	$188.40	$188.40
Purchase #5	$51.45	13.428%	$58.3587	$58.36	$58.35	$58.40
Purchase #6	$185.99	4.735%	$194.7966	$194.80	$194.80	$194.80
Purchase #7	$157.45	9.304%	$172.0991	$172.10	$172.10	$172.10
7 purchase totals =	$1,016.60		$1,090.4263	$1,090.43	$1,090.40	$1,090.50