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	$53.40	11.570%	$59.5784	$59.58	$59.60	$59.60
Purchase #2	$79.63	9.404%	$87.1184	$87.12	$87.10	$87.10
Purchase #3	$137.79	10.160%	$151.7895	$151.79	$151.80	$151.80
Purchase #4	$130.26	11.391%	$145.0979	$145.10	$145.10	$145.10
Purchase #5	$26.80	7.596%	$28.8357	$28.84	$28.85	$28.80
Purchase #6	$94.85	5.334%	$99.9093	$99.91	$99.90	$99.90
Purchase #7	$54.93	12.725%	$61.9198	$61.92	$61.90	$61.90
7 purchase totals =	$577.66		$634.2490	$634.26	$634.25	$634.20