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	$108.56	10.824%	$120.3105	$120.31	$120.30	$120.30
Purchase #2	$175.69	7.194%	$188.3291	$188.33	$188.35	$188.30
Purchase #3	$80.72	12.358%	$90.6954	$90.70	$90.70	$90.70
Purchase #4	$59.57	9.812%	$65.415	$65.42	$65.40	$65.40
Purchase #5	$7.27	4.254%	$7.5793	$7.58	$7.60	$7.60
Purchase #6	$32.84	13.106%	$37.144	$37.14	$37.15	$37.10
Purchase #7	$91.50	8.165%	$98.971	$98.97	$98.95	$99.00
7 purchase totals =	$556.15		$608.4443	$608.45	$608.45	$608.40