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	$156.65	5.710%	$165.5947	$165.59	$165.60	$165.60
Purchase #2	$112.49	3.826%	$116.7939	$116.79	$116.80	$116.80
Purchase #3	$198.45	4.818%	$208.0113	$208.01	$208.00	$208.00
Purchase #4	$191.56	10.844%	$212.3328	$212.33	$212.35	$212.30
Purchase #5	$34.36	10.274%	$37.8901	$37.89	$37.90	$37.90
Purchase #6	$104.81	12.754%	$118.1775	$118.18	$118.20	$118.20
Purchase #7	$224.47	7.842%	$242.0729	$242.07	$242.05	$242.10
7 purchase totals =	$1,022.79		$1,100.8732	$1,100.86	$1,100.90	$1,100.90