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	$224.68	7.186%	$240.8255	$240.83	$240.85	$240.80
Purchase #2	$47.52	9.452%	$52.0116	$52.01	$52.00	$52.00
Purchase #3	$25.26	12.575%	$28.4364	$28.44	$28.45	$28.40
Purchase #4	$41.25	3.753%	$42.7981	$42.80	$42.80	$42.80
Purchase #5	$39.73	13.672%	$45.1619	$45.16	$45.15	$45.20
Purchase #6	$47.76	10.496%	$52.7729	$52.77	$52.75	$52.80
Purchase #7	$70.41	3.292%	$72.7279	$72.73	$72.75	$72.70
7 purchase totals =	$496.61		$534.7343	$534.74	$534.75	$534.70