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	$242.78	10.760%	$268.9031	$268.90	$268.90	$268.90
Purchase #2	$59.68	9.486%	$65.3412	$65.34	$65.35	$65.30
Purchase #3	$163.40	13.345%	$185.2057	$185.21	$185.20	$185.20
Purchase #4	$31.40	13.401%	$35.6079	$35.61	$35.60	$35.60
Purchase #5	$87.90	7.470%	$94.4661	$94.47	$94.45	$94.50
Purchase #6	$130.52	10.597%	$144.3512	$144.35	$144.35	$144.40
Purchase #7	$143.40	3.404%	$148.2813	$148.28	$148.30	$148.30
7 purchase totals =	$859.08		$942.1565	$942.16	$942.15	$942.20