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	$144.84	12.168%	$162.4641	$162.46	$162.45	$162.50
Purchase #2	$182.95	6.167%	$194.2325	$194.23	$194.25	$194.20
Purchase #3	$76.88	6.649%	$81.9918	$81.99	$82.00	$82.00
Purchase #4	$31.27	4.196%	$32.5821	$32.58	$32.60	$32.60
Purchase #5	$170.30	7.167%	$182.5054	$182.51	$182.50	$182.50
Purchase #6	$90.53	6.734%	$96.6263	$96.63	$96.65	$96.60
Purchase #7	$82.73	11.828%	$92.5153	$92.52	$92.50	$92.50
7 purchase totals =	$779.50		$842.9175	$842.92	$842.95	$842.90