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	$86.95	6.239%	$92.3748	$92.37	$92.35	$92.40
Purchase #2	$60.66	11.727%	$67.7736	$67.77	$67.75	$67.80
Purchase #3	$70.34	10.621%	$77.8108	$77.81	$77.80	$77.80
Purchase #4	$128.96	13.393%	$146.2316	$146.23	$146.25	$146.20
Purchase #5	$99.43	10.670%	$110.0392	$110.04	$110.05	$110.00
Purchase #6	$177.77	10.719%	$196.8252	$196.83	$196.85	$196.80
Purchase #7	$170.68	10.596%	$188.7653	$188.77	$188.75	$188.80
7 purchase totals =	$794.79		$879.8205	$879.82	$879.80	$879.80