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	$180.78	8.702%	$196.5115	$196.51	$196.50	$196.50
Purchase #2	$41.80	10.244%	$46.082	$46.08	$46.10	$46.10
Purchase #3	$43.65	6.666%	$46.5597	$46.56	$46.55	$46.60
Purchase #4	$102.82	10.687%	$113.8084	$113.81	$113.80	$113.80
Purchase #5	$185.84	9.633%	$203.742	$203.74	$203.75	$203.70
Purchase #6	$112.43	5.246%	$118.3281	$118.33	$118.35	$118.30
Purchase #7	$118.40	11.200%	$131.6608	$131.66	$131.65	$131.70
7 purchase totals =	$785.72		$856.6925	$856.69	$856.70	$856.70