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	$25.31	7.799%	$27.2839	$27.28	$27.30	$27.30
Purchase #2	$73.83	6.346%	$78.5153	$78.52	$78.50	$78.50
Purchase #3	$219.92	6.249%	$233.6628	$233.66	$233.65	$233.70
Purchase #4	$117.30	6.114%	$124.4717	$124.47	$124.45	$124.50
Purchase #5	$148.53	4.689%	$155.4946	$155.49	$155.50	$155.50
Purchase #6	$82.73	13.470%	$93.8737	$93.87	$93.85	$93.90
Purchase #7	$194.84	3.426%	$201.5152	$201.52	$201.50	$201.50
7 purchase totals =	$862.46		$914.8172	$914.81	$914.75	$914.90