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	$222.82	12.521%	$250.7193	$250.72	$250.70	$250.70
Purchase #2	$219.52	5.466%	$231.519	$231.52	$231.50	$231.50
Purchase #3	$16.52	9.737%	$18.1286	$18.13	$18.15	$18.10
Purchase #4	$141.59	6.482%	$150.7679	$150.77	$150.75	$150.80
Purchase #5	$27.47	7.559%	$29.5465	$29.55	$29.55	$29.50
Purchase #6	$72.98	11.404%	$81.3026	$81.30	$81.30	$81.30
Purchase #7	$147.37	12.768%	$166.1862	$166.19	$166.20	$166.20
7 purchase totals =	$848.27		$928.1701	$928.18	$928.15	$928.10