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	$28.56	9.616%	$31.3063	$31.31	$31.30	$31.30
Purchase #2	$249.74	6.565%	$266.1354	$266.14	$266.15	$266.10
Purchase #3	$175.29	11.488%	$195.4273	$195.43	$195.45	$195.40
Purchase #4	$155.45	8.286%	$168.3306	$168.33	$168.35	$168.30
Purchase #5	$168.59	10.119%	$185.6496	$185.65	$185.65	$185.60
Purchase #6	$133.83	5.170%	$140.749	$140.75	$140.75	$140.70
Purchase #7	$33.34	3.688%	$34.5696	$34.57	$34.55	$34.60
7 purchase totals =	$944.80		$1,022.1678	$1,022.18	$1,022.20	$1,022.00