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	$159.53	12.533%	$179.5239	$179.52	$179.50	$179.50
Purchase #2	$94.65	9.574%	$103.7118	$103.71	$103.70	$103.70
Purchase #3	$92.89	6.746%	$99.1564	$99.16	$99.15	$99.20
Purchase #4	$7.80	7.339%	$8.3724	$8.37	$8.35	$8.40
Purchase #5	$29.82	6.113%	$31.6429	$31.64	$31.65	$31.60
Purchase #6	$149.94	6.382%	$159.5092	$159.51	$159.50	$159.50
Purchase #7	$84.70	13.866%	$96.4445	$96.44	$96.45	$96.40
7 purchase totals =	$619.33		$678.3611	$678.35	$678.30	$678.30