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	$78.48	12.210%	$88.0624	$88.06	$88.05	$88.10
Purchase #2	$83.59	13.212%	$94.6339	$94.63	$94.65	$94.60
Purchase #3	$78.59	4.225%	$81.9104	$81.91	$81.90	$81.90
Purchase #4	$148.60	11.738%	$166.0427	$166.04	$166.05	$166.00
Purchase #5	$192.54	3.800%	$199.8565	$199.86	$199.85	$199.90
Purchase #6	$55.45	13.356%	$62.8559	$62.86	$62.85	$62.90
Purchase #7	$145.98	3.394%	$150.9346	$150.93	$150.95	$150.90
7 purchase totals =	$783.23		$844.2964	$844.29	$844.30	$844.30