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	$7.49	5.360%	$7.8915	$7.89	$7.90	$7.90
Purchase #2	$49.30	9.250%	$53.8603	$53.86	$53.85	$53.90
Purchase #3	$75.86	4.137%	$78.9983	$79.00	$79.00	$79.00
Purchase #4	$192.94	10.673%	$213.5325	$213.53	$213.55	$213.50
Purchase #5	$63.78	13.769%	$72.5619	$72.56	$72.55	$72.60
Purchase #6	$154.94	11.129%	$172.1833	$172.18	$172.20	$172.20
Purchase #7	$243.31	9.432%	$266.259	$266.26	$266.25	$266.30
7 purchase totals =	$787.62		$865.2868	$865.28	$865.30	$865.40