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	$149.79	6.312%	$159.2447	$159.24	$159.25	$159.20
Purchase #2	$8.69	7.274%	$9.3221	$9.32	$9.30	$9.30
Purchase #3	$37.94	12.796%	$42.7948	$42.79	$42.80	$42.80
Purchase #4	$21.63	5.804%	$22.8854	$22.89	$22.90	$22.90
Purchase #5	$26.31	13.464%	$29.8524	$29.85	$29.85	$29.90
Purchase #6	$181.71	4.243%	$189.42	$189.42	$189.40	$189.40
Purchase #7	$78.82	13.628%	$89.5616	$89.56	$89.55	$89.60
7 purchase totals =	$504.89		$543.0810	$543.07	$543.05	$543.10