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	$100.57	8.405%	$109.0229	$109.02	$109.00	$109.00
Purchase #2	$151.31	11.172%	$168.2144	$168.21	$168.20	$168.20
Purchase #3	$116.99	8.666%	$127.1284	$127.13	$127.15	$127.10
Purchase #4	$192.64	9.410%	$210.7674	$210.77	$210.75	$210.80
Purchase #5	$10.74	4.679%	$11.2425	$11.24	$11.25	$11.20
Purchase #6	$174.83	4.712%	$183.068	$183.07	$183.05	$183.10
Purchase #7	$102.82	5.473%	$108.4473	$108.45	$108.45	$108.40
7 purchase totals =	$849.90		$917.8909	$917.89	$917.85	$917.80