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	$170.45	10.390%	$188.1598	$188.16	$188.15	$188.20
Purchase #2	$31.57	3.601%	$32.7068	$32.71	$32.70	$32.70
Purchase #3	$167.44	4.590%	$175.1255	$175.13	$175.15	$175.10
Purchase #4	$154.96	10.760%	$171.6337	$171.63	$171.65	$171.60
Purchase #5	$18.44	8.640%	$20.0332	$20.03	$20.05	$20.00
Purchase #6	$233.78	3.120%	$241.0739	$241.07	$241.05	$241.10
Purchase #7	$78.27	9.663%	$85.8332	$85.83	$85.85	$85.80
7 purchase totals =	$854.91		$914.5661	$914.56	$914.60	$914.50