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	$86.34	4.314%	$90.0647	$90.06	$90.05	$90.10
Purchase #2	$206.37	5.570%	$217.8648	$217.86	$217.85	$217.90
Purchase #3	$35.55	6.635%	$37.9087	$37.91	$37.90	$37.90
Purchase #4	$99.29	10.710%	$109.924	$109.92	$109.90	$109.90
Purchase #5	$80.73	3.574%	$83.6153	$83.62	$83.60	$83.60
Purchase #6	$151.80	5.439%	$160.0564	$160.06	$160.05	$160.10
Purchase #7	$114.41	10.469%	$126.3876	$126.39	$126.40	$126.40
7 purchase totals =	$774.49		$825.8215	$825.82	$825.75	$825.90