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	$225.76	3.235%	$233.0633	$233.06	$233.05	$233.10
Purchase #2	$5.78	9.131%	$6.3078	$6.31	$6.30	$6.30
Purchase #3	$227.30	13.772%	$258.6038	$258.60	$258.60	$258.60
Purchase #4	$250.86	3.530%	$259.7154	$259.72	$259.70	$259.70
Purchase #5	$199.85	13.382%	$226.5939	$226.59	$226.60	$226.60
Purchase #6	$57.49	7.223%	$61.6425	$61.64	$61.65	$61.60
Purchase #7	$36.47	4.235%	$38.0145	$38.01	$38.00	$38.00
7 purchase totals =	$1,003.51		$1,083.9412	$1,083.93	$1,083.90	$1,083.90