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	$189.75	5.389%	$199.9756	$199.98	$200.00	$200.00
Purchase #2	$56.29	6.467%	$59.9303	$59.93	$59.95	$59.90
Purchase #3	$83.85	7.769%	$90.3643	$90.36	$90.35	$90.40
Purchase #4	$127.66	11.870%	$142.8132	$142.81	$142.80	$142.80
Purchase #5	$37.54	6.595%	$40.0158	$40.02	$40.00	$40.00
Purchase #6	$210.99	5.422%	$222.4299	$222.43	$222.45	$222.40
Purchase #7	$123.66	9.616%	$135.5511	$135.55	$135.55	$135.60
7 purchase totals =	$829.74		$891.0802	$891.08	$891.10	$891.10