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	$169.69	12.131%	$190.2751	$190.28	$190.30	$190.30
Purchase #2	$34.80	11.699%	$38.8713	$38.87	$38.85	$38.90
Purchase #3	$225.90	10.425%	$249.4501	$249.45	$249.45	$249.50
Purchase #4	$168.98	13.461%	$191.7264	$191.73	$191.75	$191.70
Purchase #5	$233.77	9.454%	$255.8706	$255.87	$255.85	$255.90
Purchase #6	$69.67	12.388%	$78.3007	$78.30	$78.30	$78.30
Purchase #7	$218.97	6.650%	$233.5315	$233.53	$233.55	$233.50
7 purchase totals =	$1,121.78		$1,238.0257	$1,238.03	$1,238.05	$1,238.10