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	$101.29	13.764%	$115.2316	$115.23	$115.25	$115.20
Purchase #2	$92.30	7.479%	$99.2031	$99.20	$99.20	$99.20
Purchase #3	$166.27	3.699%	$172.4203	$172.42	$172.40	$172.40
Purchase #4	$60.82	5.843%	$64.3737	$64.37	$64.35	$64.40
Purchase #5	$227.45	5.152%	$239.1682	$239.17	$239.15	$239.20
Purchase #6	$11.91	6.670%	$12.7044	$12.70	$12.70	$12.70
Purchase #7	$100.44	3.360%	$103.8148	$103.81	$103.80	$103.80
7 purchase totals =	$760.48		$806.9161	$806.90	$806.85	$806.90