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	$135.72	7.759%	$146.2505	$146.25	$146.25	$146.30
Purchase #2	$96.66	8.802%	$105.168	$105.17	$105.15	$105.20
Purchase #3	$45.69	8.720%	$49.6742	$49.67	$49.65	$49.70
Purchase #4	$194.67	8.279%	$210.7867	$210.79	$210.80	$210.80
Purchase #5	$81.72	10.654%	$90.4264	$90.43	$90.45	$90.40
Purchase #6	$148.43	8.319%	$160.7779	$160.78	$160.80	$160.80
Purchase #7	$145.61	8.747%	$158.3465	$158.35	$158.35	$158.30
7 purchase totals =	$848.50		$921.4302	$921.44	$921.45	$921.50