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	$52.98	7.708%	$57.0637	$57.06	$57.05	$57.10
Purchase #2	$180.87	10.463%	$199.7944	$199.79	$199.80	$199.80
Purchase #3	$39.70	6.873%	$42.4286	$42.43	$42.45	$42.40
Purchase #4	$100.81	8.788%	$109.6692	$109.67	$109.65	$109.70
Purchase #5	$112.43	13.518%	$127.6283	$127.63	$127.65	$127.60
Purchase #6	$172.96	6.767%	$184.6642	$184.66	$184.65	$184.70
Purchase #7	$158.71	6.598%	$169.1817	$169.18	$169.20	$169.20
7 purchase totals =	$818.46		$890.4301	$890.42	$890.45	$890.50