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	$45.70	9.615%	$50.0941	$50.09	$50.10	$50.10
Purchase #2	$54.56	6.239%	$57.964	$57.96	$57.95	$58.00
Purchase #3	$242.83	6.752%	$259.2259	$259.23	$259.25	$259.20
Purchase #4	$85.91	12.233%	$96.4194	$96.42	$96.40	$96.40
Purchase #5	$54.72	8.132%	$59.1698	$59.17	$59.15	$59.20
Purchase #6	$114.44	3.578%	$118.5347	$118.53	$118.55	$118.50
Purchase #7	$141.69	7.692%	$152.5888	$152.59	$152.60	$152.60
7 purchase totals =	$739.85		$793.9967	$793.99	$794.00	$794.00