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	$171.95	10.421%	$189.8689	$189.87	$189.85	$189.90
Purchase #2	$250.84	5.532%	$264.7165	$264.72	$264.70	$264.70
Purchase #3	$72.28	10.481%	$79.8557	$79.86	$79.85	$79.90
Purchase #4	$236.95	12.508%	$266.5877	$266.59	$266.60	$266.60
Purchase #5	$142.79	10.309%	$157.5102	$157.51	$157.50	$157.50
Purchase #6	$134.82	11.449%	$150.2555	$150.26	$150.25	$150.30
Purchase #7	$61.79	6.829%	$66.0096	$66.01	$66.00	$66.00
7 purchase totals =	$1,071.42		$1,174.8041	$1,174.82	$1,174.75	$1,174.90