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	$225.27	10.486%	$248.8918	$248.89	$248.90	$248.90
Purchase #2	$100.26	6.614%	$106.8912	$106.89	$106.90	$106.90
Purchase #3	$33.45	13.299%	$37.8985	$37.90	$37.90	$37.90
Purchase #4	$62.25	4.141%	$64.8278	$64.83	$64.85	$64.80
Purchase #5	$34.81	3.839%	$36.1464	$36.15	$36.15	$36.10
Purchase #6	$61.68	13.805%	$70.1949	$70.19	$70.20	$70.20
Purchase #7	$73.83	7.753%	$79.554	$79.55	$79.55	$79.60
7 purchase totals =	$591.55		$644.4046	$644.40	$644.45	$644.40