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	$39.75	5.774%	$42.0452	$42.05	$42.05	$42.00
Purchase #2	$195.60	12.535%	$220.1185	$220.12	$220.10	$220.10
Purchase #3	$17.63	6.573%	$18.7888	$18.79	$18.80	$18.80
Purchase #4	$173.28	6.699%	$184.888	$184.89	$184.90	$184.90
Purchase #5	$34.73	7.545%	$37.3504	$37.35	$37.35	$37.40
Purchase #6	$36.85	6.497%	$39.2441	$39.24	$39.25	$39.20
Purchase #7	$51.70	6.496%	$55.0584	$55.06	$55.05	$55.10
7 purchase totals =	$549.54		$597.4934	$597.50	$597.50	$597.50