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	$178.36	3.395%	$184.4153	$184.42	$184.40	$184.40
Purchase #2	$102.65	3.580%	$106.3249	$106.32	$106.30	$106.30
Purchase #3	$123.54	10.360%	$136.3387	$136.34	$136.35	$136.30
Purchase #4	$169.29	5.500%	$178.601	$178.60	$178.60	$178.60
Purchase #5	$58.92	4.544%	$61.5973	$61.60	$61.60	$61.60
Purchase #6	$203.86	8.535%	$221.2595	$221.26	$221.25	$221.30
Purchase #7	$101.43	3.528%	$105.0085	$105.01	$105.00	$105.00
7 purchase totals =	$938.05		$993.5452	$993.55	$993.50	$993.50