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	$9.28	12.776%	$10.4656	$10.47	$10.45	$10.50
Purchase #2	$245.89	12.184%	$275.8492	$275.85	$275.85	$275.80
Purchase #3	$98.72	11.485%	$110.058	$110.06	$110.05	$110.10
Purchase #4	$6.62	13.149%	$7.4905	$7.49	$7.50	$7.50
Purchase #5	$191.79	12.571%	$215.8999	$215.90	$215.90	$215.90
Purchase #6	$144.49	4.537%	$151.0455	$151.05	$151.05	$151.00
Purchase #7	$8.48	11.185%	$9.4285	$9.43	$9.45	$9.40
7 purchase totals =	$705.27		$780.2372	$780.25	$780.25	$780.20