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	$249.47	10.334%	$275.2502	$275.25	$275.25	$275.30
Purchase #2	$85.41	6.308%	$90.7977	$90.80	$90.80	$90.80
Purchase #3	$31.65	12.443%	$35.5882	$35.59	$35.60	$35.60
Purchase #4	$217.98	9.402%	$238.4745	$238.47	$238.45	$238.50
Purchase #5	$158.49	5.468%	$167.1562	$167.16	$167.15	$167.20
Purchase #6	$189.80	4.563%	$198.4606	$198.46	$198.45	$198.50
Purchase #7	$68.42	10.679%	$75.7266	$75.73	$75.75	$75.70
7 purchase totals =	$1,001.22		$1,081.4540	$1,081.46	$1,081.45	$1,081.60