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	$86.89	3.310%	$89.7661	$89.77	$89.75	$89.80
Purchase #2	$80.95	10.161%	$89.1753	$89.18	$89.20	$89.20
Purchase #3	$102.80	11.477%	$114.5984	$114.60	$114.60	$114.60
Purchase #4	$218.39	10.634%	$241.6136	$241.61	$241.60	$241.60
Purchase #5	$155.97	11.844%	$174.4431	$174.44	$174.45	$174.40
Purchase #6	$123.73	5.766%	$130.8643	$130.86	$130.85	$130.90
Purchase #7	$40.43	7.179%	$43.3325	$43.33	$43.35	$43.30
7 purchase totals =	$809.16		$883.7933	$883.79	$883.80	$883.80