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	$63.35	6.191%	$67.272	$67.27	$67.25	$67.30
Purchase #2	$132.59	13.760%	$150.8344	$150.83	$150.85	$150.80
Purchase #3	$103.69	7.777%	$111.754	$111.75	$111.75	$111.80
Purchase #4	$146.53	7.421%	$157.404	$157.40	$157.40	$157.40
Purchase #5	$16.35	11.830%	$18.2842	$18.28	$18.30	$18.30
Purchase #6	$113.97	10.623%	$126.077	$126.08	$126.10	$126.10
Purchase #7	$121.33	4.154%	$126.37	$126.37	$126.35	$126.40
7 purchase totals =	$697.81		$757.9956	$757.98	$758.00	$758.10