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	$71.79	12.723%	$80.9238	$80.92	$80.90	$80.90
Purchase #2	$31.76	3.551%	$32.8878	$32.89	$32.90	$32.90
Purchase #3	$174.49	11.656%	$194.8286	$194.83	$194.85	$194.80
Purchase #4	$131.64	10.114%	$144.9541	$144.95	$144.95	$145.00
Purchase #5	$202.73	7.679%	$218.2976	$218.30	$218.30	$218.30
Purchase #6	$146.58	12.386%	$164.7354	$164.74	$164.75	$164.70
Purchase #7	$102.43	8.737%	$111.3793	$111.38	$111.40	$111.40
7 purchase totals =	$861.42		$948.0066	$948.01	$948.05	$948.00