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	$25.64	7.847%	$27.652	$27.65	$27.65	$27.70
Purchase #2	$162.51	4.191%	$169.3208	$169.32	$169.30	$169.30
Purchase #3	$12.58	7.455%	$13.5178	$13.52	$13.50	$13.50
Purchase #4	$174.63	6.424%	$185.8482	$185.85	$185.85	$185.80
Purchase #5	$67.97	6.607%	$72.4608	$72.46	$72.45	$72.50
Purchase #6	$102.53	3.200%	$105.811	$105.81	$105.80	$105.80
Purchase #7	$25.94	3.205%	$26.7714	$26.77	$26.75	$26.80
7 purchase totals =	$571.80		$601.3820	$601.38	$601.30	$601.40