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	$31.54	8.793%	$34.3133	$34.31	$34.30	$34.30
Purchase #2	$129.64	6.725%	$138.3583	$138.36	$138.35	$138.40
Purchase #3	$111.92	6.175%	$118.8311	$118.83	$118.85	$118.80
Purchase #4	$167.87	13.731%	$190.9202	$190.92	$190.90	$190.90
Purchase #5	$158.39	7.700%	$170.586	$170.59	$170.60	$170.60
Purchase #6	$52.61	6.270%	$55.9086	$55.91	$55.90	$55.90
Purchase #7	$113.57	9.132%	$123.9412	$123.94	$123.95	$123.90
7 purchase totals =	$765.54		$832.8587	$832.86	$832.85	$832.80