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	$96.29	13.359%	$109.1534	$109.15	$109.15	$109.20
Purchase #2	$51.99	12.476%	$58.4763	$58.48	$58.50	$58.50
Purchase #3	$67.38	10.701%	$74.5903	$74.59	$74.60	$74.60
Purchase #4	$53.58	10.386%	$59.1448	$59.14	$59.15	$59.10
Purchase #5	$83.52	12.294%	$93.7879	$93.79	$93.80	$93.80
Purchase #6	$89.71	7.328%	$96.2839	$96.28	$96.30	$96.30
Purchase #7	$57.27	6.208%	$60.8253	$60.83	$60.85	$60.80
7 purchase totals =	$499.74		$552.2619	$552.26	$552.35	$552.30