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	$93.70	6.345%	$99.6453	$99.65	$99.65	$99.60
Purchase #2	$144.47	5.443%	$152.3335	$152.33	$152.35	$152.30
Purchase #3	$128.61	4.127%	$133.9177	$133.92	$133.90	$133.90
Purchase #4	$53.66	10.504%	$59.2964	$59.30	$59.30	$59.30
Purchase #5	$99.69	9.651%	$109.3111	$109.31	$109.30	$109.30
Purchase #6	$156.81	10.704%	$173.5949	$173.59	$173.60	$173.60
Purchase #7	$250.91	11.428%	$279.584	$279.58	$279.60	$279.60
7 purchase totals =	$927.85		$1,007.6829	$1,007.68	$1,007.70	$1,007.60