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	$17.93	10.487%	$19.8103	$19.81	$19.80	$19.80
Purchase #2	$228.35	3.690%	$236.7761	$236.78	$236.80	$236.80
Purchase #3	$75.56	3.718%	$78.3693	$78.37	$78.35	$78.40
Purchase #4	$199.32	8.428%	$216.1187	$216.12	$216.10	$216.10
Purchase #5	$170.64	8.457%	$185.071	$185.07	$185.05	$185.10
Purchase #6	$87.42	5.110%	$91.8872	$91.89	$91.90	$91.90
Purchase #7	$80.60	7.449%	$86.6039	$86.60	$86.60	$86.60
7 purchase totals =	$859.82		$914.6365	$914.64	$914.60	$914.70