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	$90.55	4.356%	$94.4944	$94.49	$94.50	$94.50
Purchase #2	$115.58	10.600%	$127.8315	$127.83	$127.85	$127.80
Purchase #3	$151.85	10.281%	$167.4617	$167.46	$167.45	$167.50
Purchase #4	$8.76	9.240%	$9.5694	$9.57	$9.55	$9.60
Purchase #5	$39.57	7.542%	$42.5544	$42.55	$42.55	$42.60
Purchase #6	$20.72	5.102%	$21.7771	$21.78	$21.80	$21.80
Purchase #7	$125.73	7.520%	$135.1849	$135.18	$135.20	$135.20
7 purchase totals =	$552.76		$598.8734	$598.86	$598.90	$599.00