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	$224.90	4.708%	$235.4883	$235.49	$235.50	$235.50
Purchase #2	$226.67	13.654%	$257.6195	$257.62	$257.60	$257.60
Purchase #3	$196.72	6.630%	$209.7625	$209.76	$209.75	$209.80
Purchase #4	$10.79	4.556%	$11.2816	$11.28	$11.30	$11.30
Purchase #5	$50.26	7.610%	$54.0848	$54.08	$54.10	$54.10
Purchase #6	$83.61	7.295%	$89.7093	$89.71	$89.70	$89.70
Purchase #7	$136.62	6.184%	$145.0686	$145.07	$145.05	$145.10
7 purchase totals =	$929.57		$1,003.0146	$1,003.01	$1,003.00	$1,003.10