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	$236.54	12.855%	$266.9472	$266.95	$266.95	$266.90
Purchase #2	$106.55	5.378%	$112.2803	$112.28	$112.30	$112.30
Purchase #3	$189.44	3.465%	$196.0041	$196.00	$196.00	$196.00
Purchase #4	$71.53	10.408%	$78.9748	$78.97	$78.95	$79.00
Purchase #5	$14.46	5.675%	$15.2806	$15.28	$15.30	$15.30
Purchase #6	$107.76	3.763%	$111.815	$111.82	$111.80	$111.80
Purchase #7	$35.83	5.261%	$37.715	$37.72	$37.70	$37.70
7 purchase totals =	$762.11		$819.0170	$819.02	$819.00	$819.00