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	$165.97	10.257%	$182.9935	$182.99	$183.00	$183.00
Purchase #2	$160.97	12.183%	$180.581	$180.58	$180.60	$180.60
Purchase #3	$198.30	8.351%	$214.86	$214.86	$214.85	$214.90
Purchase #4	$74.46	12.500%	$83.7675	$83.77	$83.75	$83.80
Purchase #5	$172.75	8.515%	$187.4597	$187.46	$187.45	$187.50
Purchase #6	$20.33	6.454%	$21.6421	$21.64	$21.65	$21.60
Purchase #7	$124.45	5.518%	$131.3172	$131.32	$131.30	$131.30
7 purchase totals =	$917.23		$1,002.6210	$1,002.62	$1,002.60	$1,002.70