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	$75.76	5.759%	$80.123	$80.12	$80.10	$80.10
Purchase #2	$244.80	8.768%	$266.2641	$266.26	$266.25	$266.30
Purchase #3	$126.27	6.828%	$134.8917	$134.89	$134.90	$134.90
Purchase #4	$112.45	13.549%	$127.6859	$127.69	$127.70	$127.70
Purchase #5	$192.65	10.806%	$213.4678	$213.47	$213.45	$213.50
Purchase #6	$32.56	9.210%	$35.5588	$35.56	$35.55	$35.60
Purchase #7	$130.28	8.452%	$141.2913	$141.29	$141.30	$141.30
7 purchase totals =	$914.77		$999.2826	$999.28	$999.25	$999.40