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	$180.83	10.284%	$199.4266	$199.43	$199.45	$199.40
Purchase #2	$179.76	10.852%	$199.2676	$199.27	$199.25	$199.30
Purchase #3	$109.51	13.636%	$124.4428	$124.44	$124.45	$124.40
Purchase #4	$30.28	13.675%	$34.4208	$34.42	$34.40	$34.40
Purchase #5	$69.88	12.755%	$78.7932	$78.79	$78.80	$78.80
Purchase #6	$133.96	6.609%	$142.8134	$142.81	$142.80	$142.80
Purchase #7	$38.59	10.803%	$42.7589	$42.76	$42.75	$42.80
7 purchase totals =	$742.81		$821.9233	$821.92	$821.90	$821.90