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	$152.82	10.287%	$168.5406	$168.54	$168.55	$168.50
Purchase #2	$55.92	8.143%	$60.4736	$60.47	$60.45	$60.50
Purchase #3	$199.40	11.152%	$221.6371	$221.64	$221.65	$221.60
Purchase #4	$178.93	12.108%	$200.5948	$200.59	$200.60	$200.60
Purchase #5	$143.75	8.572%	$156.0723	$156.07	$156.05	$156.10
Purchase #6	$179.45	5.849%	$189.946	$189.95	$189.95	$189.90
Purchase #7	$81.84	11.465%	$91.223	$91.22	$91.20	$91.20
7 purchase totals =	$992.11		$1,088.4874	$1,088.48	$1,088.45	$1,088.40