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	$54.81	11.703%	$61.2244	$61.22	$61.20	$61.20
Purchase #2	$75.65	13.689%	$86.0057	$86.01	$86.00	$86.00
Purchase #3	$25.79	12.595%	$29.0383	$29.04	$29.05	$29.00
Purchase #4	$154.54	11.678%	$172.5872	$172.59	$172.60	$172.60
Purchase #5	$192.32	4.133%	$200.2686	$200.27	$200.25	$200.30
Purchase #6	$128.89	10.300%	$142.1657	$142.17	$142.15	$142.20
Purchase #7	$27.87	4.104%	$29.0138	$29.01	$29.00	$29.00
7 purchase totals =	$659.87		$720.3037	$720.31	$720.25	$720.30