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	$108.52	11.351%	$120.8381	$120.84	$120.85	$120.80
Purchase #2	$247.65	10.386%	$273.3709	$273.37	$273.35	$273.40
Purchase #3	$133.33	9.790%	$146.383	$146.38	$146.40	$146.40
Purchase #4	$80.28	12.485%	$90.303	$90.30	$90.30	$90.30
Purchase #5	$226.40	6.715%	$241.6028	$241.60	$241.60	$241.60
Purchase #6	$214.55	6.511%	$228.5194	$228.52	$228.50	$228.50
Purchase #7	$146.65	13.593%	$166.5841	$166.58	$166.60	$166.60
7 purchase totals =	$1,157.38		$1,267.6013	$1,267.59	$1,267.60	$1,267.60