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	$145.98	5.154%	$153.5038	$153.50	$153.50	$153.50
Purchase #2	$180.31	6.294%	$191.6587	$191.66	$191.65	$191.70
Purchase #3	$158.72	9.795%	$174.2666	$174.27	$174.25	$174.30
Purchase #4	$184.53	4.272%	$192.4131	$192.41	$192.40	$192.40
Purchase #5	$52.36	5.847%	$55.4215	$55.42	$55.40	$55.40
Purchase #6	$66.46	5.873%	$70.3632	$70.36	$70.35	$70.40
Purchase #7	$66.42	7.278%	$71.254	$71.25	$71.25	$71.30
7 purchase totals =	$854.78		$908.8809	$908.87	$908.80	$909.00