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	$25.77	10.224%	$28.4047	$28.40	$28.40	$28.40
Purchase #2	$187.84	4.137%	$195.6109	$195.61	$195.60	$195.60
Purchase #3	$48.73	10.721%	$53.9543	$53.95	$53.95	$54.00
Purchase #4	$77.78	9.433%	$85.117	$85.12	$85.10	$85.10
Purchase #5	$116.37	3.457%	$120.3929	$120.39	$120.40	$120.40
Purchase #6	$198.60	6.678%	$211.8625	$211.86	$211.85	$211.90
Purchase #7	$91.55	9.385%	$100.142	$100.14	$100.15	$100.10
7 purchase totals =	$746.64		$795.4843	$795.47	$795.45	$795.50