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	$124.90	5.443%	$131.6983	$131.70	$131.70	$131.70
Purchase #2	$56.42	5.198%	$59.3527	$59.35	$59.35	$59.40
Purchase #3	$123.90	7.804%	$133.5692	$133.57	$133.55	$133.60
Purchase #4	$91.77	8.467%	$99.5402	$99.54	$99.55	$99.50
Purchase #5	$131.60	5.521%	$138.8656	$138.87	$138.85	$138.90
Purchase #6	$172.55	6.306%	$183.431	$183.43	$183.45	$183.40
Purchase #7	$178.38	7.776%	$192.2508	$192.25	$192.25	$192.30
7 purchase totals =	$879.52		$938.7078	$938.71	$938.70	$938.80