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	$114.98	12.736%	$129.6239	$129.62	$129.60	$129.60
Purchase #2	$223.59	8.255%	$242.0474	$242.05	$242.05	$242.00
Purchase #3	$150.28	12.406%	$168.9237	$168.92	$168.90	$168.90
Purchase #4	$45.89	8.686%	$49.876	$49.88	$49.90	$49.90
Purchase #5	$127.94	3.348%	$132.2234	$132.22	$132.20	$132.20
Purchase #6	$37.81	11.840%	$42.2867	$42.29	$42.30	$42.30
Purchase #7	$159.32	9.398%	$174.2929	$174.29	$174.30	$174.30
7 purchase totals =	$859.81		$939.2740	$939.27	$939.25	$939.20