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	$86.89	3.115%	$89.5966	$89.60	$89.60	$89.60
Purchase #2	$174.77	5.473%	$184.3352	$184.34	$184.35	$184.30
Purchase #3	$174.42	10.320%	$192.4201	$192.42	$192.40	$192.40
Purchase #4	$176.78	13.385%	$200.442	$200.44	$200.45	$200.40
Purchase #5	$85.42	4.469%	$89.2374	$89.24	$89.25	$89.20
Purchase #6	$165.99	8.572%	$180.2187	$180.22	$180.20	$180.20
Purchase #7	$215.45	9.366%	$235.629	$235.63	$235.65	$235.60
7 purchase totals =	$1,079.72		$1,171.8790	$1,171.89	$1,171.90	$1,171.70