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	$18.85	10.227%	$20.7778	$20.78	$20.80	$20.80
Purchase #2	$65.25	3.509%	$67.5396	$67.54	$67.55	$67.50
Purchase #3	$69.83	4.374%	$72.8844	$72.88	$72.90	$72.90
Purchase #4	$22.78	4.222%	$23.7418	$23.74	$23.75	$23.70
Purchase #5	$143.78	4.374%	$150.0689	$150.07	$150.05	$150.10
Purchase #6	$140.51	7.499%	$151.0468	$151.05	$151.05	$151.00
Purchase #7	$188.46	9.220%	$205.836	$205.84	$205.85	$205.80
7 purchase totals =	$649.46		$691.8953	$691.90	$691.95	$691.80