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	$141.86	6.329%	$150.8383	$150.84	$150.85	$150.80
Purchase #2	$223.77	6.228%	$237.7064	$237.71	$237.70	$237.70
Purchase #3	$177.80	8.345%	$192.6374	$192.64	$192.65	$192.60
Purchase #4	$145.58	4.727%	$152.4616	$152.46	$152.45	$152.50
Purchase #5	$56.82	8.176%	$61.4656	$61.47	$61.45	$61.50
Purchase #6	$160.38	11.633%	$179.037	$179.04	$179.05	$179.00
Purchase #7	$19.52	6.210%	$20.7322	$20.73	$20.75	$20.70
7 purchase totals =	$925.73		$994.8785	$994.89	$994.90	$994.80