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	$227.69	3.736%	$236.1965	$236.20	$236.20	$236.20
Purchase #2	$204.32	9.683%	$224.1043	$224.10	$224.10	$224.10
Purchase #3	$33.96	9.140%	$37.0639	$37.06	$37.05	$37.10
Purchase #4	$103.56	4.741%	$108.4698	$108.47	$108.45	$108.50
Purchase #5	$201.86	3.770%	$209.4701	$209.47	$209.45	$209.50
Purchase #6	$56.49	5.191%	$59.4224	$59.42	$59.40	$59.40
Purchase #7	$85.65	12.158%	$96.0633	$96.06	$96.05	$96.10
7 purchase totals =	$913.53		$970.7903	$970.78	$970.70	$970.90