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	$36.61	10.572%	$40.4804	$40.48	$40.50	$40.50
Purchase #2	$34.80	7.475%	$37.4013	$37.40	$37.40	$37.40
Purchase #3	$37.84	6.697%	$40.3741	$40.37	$40.35	$40.40
Purchase #4	$50.76	7.834%	$54.7365	$54.74	$54.75	$54.70
Purchase #5	$195.82	6.251%	$208.0607	$208.06	$208.05	$208.10
Purchase #6	$150.67	12.712%	$169.8232	$169.82	$169.80	$169.80
Purchase #7	$5.38	13.346%	$6.098	$6.10	$6.10	$6.10
7 purchase totals =	$511.88		$556.9742	$556.97	$556.95	$557.00