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	$121.45	7.282%	$130.294	$130.29	$130.30	$130.30
Purchase #2	$139.79	4.204%	$145.6668	$145.67	$145.65	$145.70
Purchase #3	$215.92	3.667%	$223.8378	$223.84	$223.85	$223.80
Purchase #4	$127.86	11.663%	$142.7723	$142.77	$142.75	$142.80
Purchase #5	$207.52	5.311%	$218.5414	$218.54	$218.55	$218.50
Purchase #6	$92.97	7.308%	$99.7642	$99.76	$99.75	$99.80
Purchase #7	$31.58	12.662%	$35.5787	$35.58	$35.60	$35.60
7 purchase totals =	$937.09		$996.4552	$996.45	$996.45	$996.50