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	$22.70	12.543%	$25.5473	$25.55	$25.55	$25.50
Purchase #2	$232.71	11.671%	$259.8696	$259.87	$259.85	$259.90
Purchase #3	$173.78	6.597%	$185.2443	$185.24	$185.25	$185.20
Purchase #4	$33.70	8.408%	$36.5335	$36.53	$36.55	$36.50
Purchase #5	$211.95	12.729%	$238.9291	$238.93	$238.95	$238.90
Purchase #6	$53.33	13.251%	$60.3968	$60.40	$60.40	$60.40
Purchase #7	$250.49	11.696%	$279.7873	$279.79	$279.80	$279.80
7 purchase totals =	$978.66		$1,086.3079	$1,086.31	$1,086.35	$1,086.20