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	$128.51	13.851%	$146.3099	$146.31	$146.30	$146.30
Purchase #2	$61.27	6.805%	$65.4394	$65.44	$65.45	$65.40
Purchase #3	$89.69	7.549%	$96.4607	$96.46	$96.45	$96.50
Purchase #4	$234.96	8.866%	$255.7916	$255.79	$255.80	$255.80
Purchase #5	$136.53	9.584%	$149.615	$149.62	$149.60	$149.60
Purchase #6	$152.46	13.288%	$172.7189	$172.72	$172.70	$172.70
Purchase #7	$48.57	6.873%	$51.9082	$51.91	$51.90	$51.90
7 purchase totals =	$851.99		$938.2437	$938.25	$938.20	$938.20