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	$83.96	3.142%	$86.598	$86.60	$86.60	$86.60
Purchase #2	$85.27	7.789%	$91.9117	$91.91	$91.90	$91.90
Purchase #3	$153.88	10.586%	$170.1697	$170.17	$170.15	$170.20
Purchase #4	$18.27	4.774%	$19.1422	$19.14	$19.15	$19.10
Purchase #5	$109.31	13.355%	$123.9084	$123.91	$123.90	$123.90
Purchase #6	$233.72	12.712%	$263.4305	$263.43	$263.45	$263.40
Purchase #7	$22.48	10.653%	$24.8748	$24.87	$24.85	$24.90
7 purchase totals =	$706.89		$780.0353	$780.03	$780.00	$780.00