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	$232.58	3.378%	$240.4366	$240.44	$240.45	$240.40
Purchase #2	$91.73	12.525%	$103.2192	$103.22	$103.20	$103.20
Purchase #3	$94.52	7.614%	$101.7168	$101.72	$101.70	$101.70
Purchase #4	$165.61	4.292%	$172.718	$172.72	$172.70	$172.70
Purchase #5	$206.39	10.254%	$227.5532	$227.55	$227.55	$227.60
Purchase #6	$37.61	6.224%	$39.9508	$39.95	$39.95	$40.00
Purchase #7	$145.89	5.585%	$154.038	$154.04	$154.05	$154.00
7 purchase totals =	$974.33		$1,039.6326	$1,039.64	$1,039.60	$1,039.60