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	$28.51	3.834%	$29.6031	$29.60	$29.60	$29.60
Purchase #2	$33.79	6.229%	$35.8948	$35.89	$35.90	$35.90
Purchase #3	$244.42	13.460%	$277.3189	$277.32	$277.30	$277.30
Purchase #4	$46.62	9.142%	$50.882	$50.88	$50.90	$50.90
Purchase #5	$86.95	10.147%	$95.7728	$95.77	$95.75	$95.80
Purchase #6	$78.64	4.220%	$81.9586	$81.96	$81.95	$82.00
Purchase #7	$191.34	12.542%	$215.3379	$215.34	$215.35	$215.30
7 purchase totals =	$710.27		$786.7681	$786.76	$786.75	$786.80