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	$87.31	6.396%	$92.8943	$92.89	$92.90	$92.90
Purchase #2	$39.49	5.830%	$41.7923	$41.79	$41.80	$41.80
Purchase #3	$123.67	13.752%	$140.6771	$140.68	$140.70	$140.70
Purchase #4	$86.58	3.648%	$89.7384	$89.74	$89.75	$89.70
Purchase #5	$46.46	6.113%	$49.3001	$49.30	$49.30	$49.30
Purchase #6	$45.94	6.476%	$48.9151	$48.92	$48.90	$48.90
Purchase #7	$211.83	13.413%	$240.2428	$240.24	$240.25	$240.20
7 purchase totals =	$641.28		$703.5601	$703.56	$703.60	$703.50