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	$242.41	12.746%	$273.3076	$273.31	$273.30	$273.30
Purchase #2	$52.40	3.319%	$54.1392	$54.14	$54.15	$54.10
Purchase #3	$119.28	9.114%	$130.1512	$130.15	$130.15	$130.20
Purchase #4	$139.68	4.261%	$145.6318	$145.63	$145.65	$145.60
Purchase #5	$83.52	9.871%	$91.7643	$91.76	$91.75	$91.80
Purchase #6	$141.53	5.807%	$149.7486	$149.75	$149.75	$149.70
Purchase #7	$151.76	8.627%	$164.8523	$164.85	$164.85	$164.90
7 purchase totals =	$930.58		$1,009.5950	$1,009.59	$1,009.60	$1,009.60