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	$18.33	3.259%	$18.9274	$18.93	$18.95	$18.90
Purchase #2	$244.84	3.539%	$253.5049	$253.50	$253.50	$253.50
Purchase #3	$153.57	3.459%	$158.882	$158.88	$158.90	$158.90
Purchase #4	$238.31	8.356%	$258.2232	$258.22	$258.20	$258.20
Purchase #5	$29.69	12.690%	$33.4577	$33.46	$33.45	$33.50
Purchase #6	$77.77	3.749%	$80.6856	$80.69	$80.70	$80.70
Purchase #7	$131.27	5.516%	$138.5109	$138.51	$138.50	$138.50
7 purchase totals =	$893.78		$942.1917	$942.19	$942.20	$942.20