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	$121.50	4.834%	$127.3733	$127.37	$127.35	$127.40
Purchase #2	$182.44	11.233%	$202.9335	$202.93	$202.95	$202.90
Purchase #3	$131.89	5.475%	$139.111	$139.11	$139.10	$139.10
Purchase #4	$52.75	6.167%	$56.0031	$56.00	$56.00	$56.00
Purchase #5	$176.41	8.574%	$191.5354	$191.54	$191.55	$191.50
Purchase #6	$167.72	13.293%	$190.015	$190.02	$190.00	$190.00
Purchase #7	$223.87	12.281%	$251.3635	$251.36	$251.35	$251.40
7 purchase totals =	$1,056.58		$1,158.3348	$1,158.33	$1,158.30	$1,158.30