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	$19.26	7.271%	$20.6604	$20.66	$20.65	$20.70
Purchase #2	$150.70	13.822%	$171.5298	$171.53	$171.55	$171.50
Purchase #3	$225.67	12.182%	$253.1611	$253.16	$253.15	$253.20
Purchase #4	$136.31	3.665%	$141.3058	$141.31	$141.30	$141.30
Purchase #5	$167.96	10.498%	$185.5924	$185.59	$185.60	$185.60
Purchase #6	$148.46	12.226%	$166.6107	$166.61	$166.60	$166.60
Purchase #7	$166.69	6.791%	$178.0099	$178.01	$178.00	$178.00
7 purchase totals =	$1,015.05		$1,116.8701	$1,116.87	$1,116.85	$1,116.90