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	$56.91	12.537%	$64.0448	$64.04	$64.05	$64.00
Purchase #2	$28.70	12.340%	$32.2416	$32.24	$32.25	$32.20
Purchase #3	$36.87	9.761%	$40.4689	$40.47	$40.45	$40.50
Purchase #4	$138.78	4.556%	$145.1028	$145.10	$145.10	$145.10
Purchase #5	$59.91	13.227%	$67.8343	$67.83	$67.85	$67.80
Purchase #6	$151.86	9.185%	$165.8083	$165.81	$165.80	$165.80
Purchase #7	$64.82	6.492%	$69.0281	$69.03	$69.05	$69.00
7 purchase totals =	$537.85		$584.5288	$584.52	$584.55	$584.40