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	$57.55	6.809%	$61.4686	$61.47	$61.45	$61.50
Purchase #2	$186.75	9.125%	$203.7909	$203.79	$203.80	$203.80
Purchase #3	$74.68	10.475%	$82.5027	$82.50	$82.50	$82.50
Purchase #4	$219.94	4.243%	$229.2721	$229.27	$229.25	$229.30
Purchase #5	$73.52	8.116%	$79.4869	$79.49	$79.50	$79.50
Purchase #6	$96.36	4.326%	$100.5285	$100.53	$100.55	$100.50
Purchase #7	$133.98	4.586%	$140.1243	$140.12	$140.10	$140.10
7 purchase totals =	$842.78		$897.1740	$897.17	$897.15	$897.20