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	$219.74	12.585%	$247.3943	$247.39	$247.40	$247.40
Purchase #2	$32.99	12.314%	$37.0524	$37.05	$37.05	$37.10
Purchase #3	$169.87	11.498%	$189.4017	$189.40	$189.40	$189.40
Purchase #4	$59.54	10.194%	$65.6095	$65.61	$65.60	$65.60
Purchase #5	$209.46	4.587%	$219.0679	$219.07	$219.05	$219.10
Purchase #6	$56.84	11.871%	$63.5875	$63.59	$63.60	$63.60
Purchase #7	$138.57	12.557%	$155.9702	$155.97	$155.95	$156.00
7 purchase totals =	$887.01		$978.0835	$978.08	$978.05	$978.20