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	$122.50	7.173%	$131.2869	$131.29	$131.30	$131.30
Purchase #2	$191.30	11.299%	$212.915	$212.92	$212.90	$212.90
Purchase #3	$38.52	8.461%	$41.7792	$41.78	$41.80	$41.80
Purchase #4	$85.60	5.436%	$90.2532	$90.25	$90.25	$90.30
Purchase #5	$134.47	10.472%	$148.5517	$148.55	$148.55	$148.60
Purchase #6	$52.61	6.311%	$55.9302	$55.93	$55.95	$55.90
Purchase #7	$209.82	10.349%	$231.5343	$231.53	$231.55	$231.50
7 purchase totals =	$834.82		$912.2505	$912.25	$912.30	$912.30