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	$101.64	9.618%	$111.4157	$111.42	$111.40	$111.40
Purchase #2	$241.78	9.368%	$264.43	$264.43	$264.45	$264.40
Purchase #3	$59.96	3.105%	$61.8218	$61.82	$61.80	$61.80
Purchase #4	$246.69	12.588%	$277.7433	$277.74	$277.75	$277.70
Purchase #5	$96.55	12.122%	$108.2538	$108.25	$108.25	$108.30
Purchase #6	$120.84	13.735%	$137.4374	$137.44	$137.45	$137.40
Purchase #7	$242.55	12.856%	$273.7322	$273.73	$273.75	$273.70
7 purchase totals =	$1,110.01		$1,234.8342	$1,234.83	$1,234.85	$1,234.70