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	$5.45	8.145%	$5.8939	$5.89	$5.90	$5.90
Purchase #2	$245.40	12.342%	$275.6873	$275.69	$275.70	$275.70
Purchase #3	$42.84	5.231%	$45.081	$45.08	$45.10	$45.10
Purchase #4	$43.54	3.118%	$44.8976	$44.90	$44.90	$44.90
Purchase #5	$155.40	7.388%	$166.881	$166.88	$166.90	$166.90
Purchase #6	$158.68	4.587%	$165.9587	$165.96	$165.95	$166.00
Purchase #7	$81.98	8.704%	$89.1155	$89.12	$89.10	$89.10
7 purchase totals =	$733.29		$793.5150	$793.52	$793.55	$793.60