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	$101.96	10.745%	$112.9156	$112.92	$112.90	$112.90
Purchase #2	$176.95	13.192%	$200.2932	$200.29	$200.30	$200.30
Purchase #3	$120.87	10.408%	$133.4501	$133.45	$133.45	$133.50
Purchase #4	$130.76	11.842%	$146.2446	$146.24	$146.25	$146.20
Purchase #5	$35.51	9.557%	$38.9037	$38.90	$38.90	$38.90
Purchase #6	$8.59	9.784%	$9.4304	$9.43	$9.45	$9.40
Purchase #7	$59.93	6.606%	$63.889	$63.89	$63.90	$63.90
7 purchase totals =	$634.57		$705.1266	$705.12	$705.15	$705.10