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	$28.64	7.781%	$30.8685	$30.87	$30.85	$30.90
Purchase #2	$19.71	9.540%	$21.5903	$21.59	$21.60	$21.60
Purchase #3	$152.79	3.796%	$158.5899	$158.59	$158.60	$158.60
Purchase #4	$35.58	7.678%	$38.3118	$38.31	$38.30	$38.30
Purchase #5	$137.81	13.327%	$156.1759	$156.18	$156.20	$156.20
Purchase #6	$82.89	9.736%	$90.9602	$90.96	$90.95	$91.00
Purchase #7	$113.98	11.211%	$126.7583	$126.76	$126.75	$126.80
7 purchase totals =	$571.40		$623.2549	$623.26	$623.25	$623.40