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	$239.96	10.316%	$264.7143	$264.71	$264.70	$264.70
Purchase #2	$238.71	10.759%	$264.3928	$264.39	$264.40	$264.40
Purchase #3	$36.35	11.280%	$40.4503	$40.45	$40.45	$40.50
Purchase #4	$137.49	8.499%	$149.1753	$149.18	$149.20	$149.20
Purchase #5	$173.60	7.644%	$186.87	$186.87	$186.85	$186.90
Purchase #6	$146.31	4.143%	$152.3716	$152.37	$152.35	$152.40
Purchase #7	$83.50	7.568%	$89.8193	$89.82	$89.80	$89.80
7 purchase totals =	$1,055.92		$1,147.7936	$1,147.79	$1,147.75	$1,147.90