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	$178.78	5.592%	$188.7774	$188.78	$188.80	$188.80
Purchase #2	$144.47	3.764%	$149.9079	$149.91	$149.90	$149.90
Purchase #3	$103.32	7.624%	$111.1971	$111.20	$111.20	$111.20
Purchase #4	$19.35	6.765%	$20.659	$20.66	$20.65	$20.70
Purchase #5	$115.76	4.223%	$120.6485	$120.65	$120.65	$120.60
Purchase #6	$65.63	6.851%	$70.1263	$70.13	$70.15	$70.10
Purchase #7	$156.64	9.700%	$171.8341	$171.83	$171.85	$171.80
7 purchase totals =	$783.95		$833.1503	$833.16	$833.20	$833.10