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	$29.39	9.113%	$32.0683	$32.07	$32.05	$32.10
Purchase #2	$106.31	6.840%	$113.5816	$113.58	$113.60	$113.60
Purchase #3	$98.28	11.199%	$109.2864	$109.29	$109.30	$109.30
Purchase #4	$47.87	10.231%	$52.7676	$52.77	$52.75	$52.80
Purchase #5	$37.80	11.861%	$42.2835	$42.28	$42.30	$42.30
Purchase #6	$91.67	10.330%	$101.1395	$101.14	$101.15	$101.10
Purchase #7	$118.48	11.208%	$131.7592	$131.76	$131.75	$131.80
7 purchase totals =	$529.80		$582.8861	$582.89	$582.90	$583.00