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	$222.94	12.613%	$251.0594	$251.06	$251.05	$251.10
Purchase #2	$59.54	8.118%	$64.3735	$64.37	$64.35	$64.40
Purchase #3	$237.83	7.622%	$255.9574	$255.96	$255.95	$256.00
Purchase #4	$179.48	3.334%	$185.4639	$185.46	$185.45	$185.50
Purchase #5	$243.83	6.657%	$260.0618	$260.06	$260.05	$260.10
Purchase #6	$161.48	10.786%	$178.8972	$178.90	$178.90	$178.90
Purchase #7	$127.66	3.142%	$131.6711	$131.67	$131.65	$131.70
7 purchase totals =	$1,232.76		$1,327.4843	$1,327.48	$1,327.40	$1,327.70