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	$100.98	11.301%	$112.3917	$112.39	$112.40	$112.40
Purchase #2	$188.51	10.755%	$208.7843	$208.78	$208.80	$208.80
Purchase #3	$111.84	6.638%	$119.2639	$119.26	$119.25	$119.30
Purchase #4	$250.85	6.677%	$267.5993	$267.60	$267.60	$267.60
Purchase #5	$101.51	11.362%	$113.0436	$113.04	$113.05	$113.00
Purchase #6	$46.54	5.666%	$49.177	$49.18	$49.20	$49.20
Purchase #7	$171.92	7.689%	$185.1389	$185.14	$185.15	$185.10
7 purchase totals =	$972.15		$1,055.3987	$1,055.39	$1,055.45	$1,055.40