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	$75.72	4.800%	$79.3546	$79.35	$79.35	$79.40
Purchase #2	$117.96	11.462%	$131.4806	$131.48	$131.50	$131.50
Purchase #3	$115.44	12.730%	$130.1355	$130.14	$130.15	$130.10
Purchase #4	$126.98	4.376%	$132.5366	$132.54	$132.55	$132.50
Purchase #5	$203.42	9.486%	$222.7164	$222.72	$222.70	$222.70
Purchase #6	$57.83	12.596%	$65.1143	$65.11	$65.10	$65.10
Purchase #7	$132.50	12.106%	$148.5405	$148.54	$148.55	$148.50
7 purchase totals =	$829.85		$909.8785	$909.88	$909.90	$909.80