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	$54.52	12.650%	$61.4168	$61.42	$61.40	$61.40
Purchase #2	$112.67	11.725%	$125.8806	$125.88	$125.90	$125.90
Purchase #3	$163.56	10.308%	$180.4198	$180.42	$180.40	$180.40
Purchase #4	$86.95	5.534%	$91.7618	$91.76	$91.75	$91.80
Purchase #5	$56.53	4.442%	$59.0411	$59.04	$59.05	$59.00
Purchase #6	$127.44	4.669%	$133.3902	$133.39	$133.40	$133.40
Purchase #7	$178.79	11.293%	$198.9808	$198.98	$199.00	$199.00
7 purchase totals =	$780.46		$850.8911	$850.89	$850.90	$850.90