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	$183.27	3.553%	$189.7816	$189.78	$189.80	$189.80
Purchase #2	$139.53	10.266%	$153.8541	$153.85	$153.85	$153.90
Purchase #3	$98.47	12.734%	$111.0092	$111.01	$111.00	$111.00
Purchase #4	$209.61	11.776%	$234.2937	$234.29	$234.30	$234.30
Purchase #5	$31.90	3.528%	$33.0254	$33.03	$33.05	$33.00
Purchase #6	$41.85	10.259%	$46.1434	$46.14	$46.15	$46.10
Purchase #7	$152.37	13.376%	$172.751	$172.75	$172.75	$172.80
7 purchase totals =	$857.00		$940.8584	$940.85	$940.90	$940.90