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	$150.66	13.216%	$170.5712	$170.57	$170.55	$170.60
Purchase #2	$42.97	11.715%	$48.0039	$48.00	$48.00	$48.00
Purchase #3	$168.72	9.216%	$184.2692	$184.27	$184.25	$184.30
Purchase #4	$95.63	5.470%	$100.861	$100.86	$100.85	$100.90
Purchase #5	$229.60	11.342%	$255.6412	$255.64	$255.65	$255.60
Purchase #6	$184.82	13.600%	$209.9555	$209.96	$209.95	$210.00
Purchase #7	$12.43	11.664%	$13.8798	$13.88	$13.90	$13.90
7 purchase totals =	$884.83		$983.1818	$983.18	$983.15	$983.30