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	$26.31	6.356%	$27.9823	$27.98	$28.00	$28.00
Purchase #2	$158.50	5.862%	$167.7913	$167.79	$167.80	$167.80
Purchase #3	$79.65	3.530%	$82.4616	$82.46	$82.45	$82.50
Purchase #4	$74.44	12.710%	$83.9013	$83.90	$83.90	$83.90
Purchase #5	$234.51	7.392%	$251.845	$251.85	$251.85	$251.80
Purchase #6	$67.87	5.386%	$71.5255	$71.53	$71.55	$71.50
Purchase #7	$61.79	7.412%	$66.3699	$66.37	$66.35	$66.40
7 purchase totals =	$703.07		$751.8769	$751.88	$751.90	$751.90