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	$19.42	7.617%	$20.8992	$20.90	$20.90	$20.90
Purchase #2	$246.76	10.742%	$273.267	$273.27	$273.25	$273.30
Purchase #3	$189.82	13.778%	$215.9734	$215.97	$215.95	$216.00
Purchase #4	$53.71	4.501%	$56.1275	$56.13	$56.15	$56.10
Purchase #5	$206.78	10.619%	$228.738	$228.74	$228.75	$228.70
Purchase #6	$18.40	13.636%	$20.909	$20.91	$20.90	$20.90
Purchase #7	$113.33	10.220%	$124.9123	$124.91	$124.90	$124.90
7 purchase totals =	$848.22		$940.8264	$940.83	$940.80	$940.80