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	$134.99	5.709%	$142.6966	$142.70	$142.70	$142.70
Purchase #2	$167.59	10.666%	$185.4651	$185.47	$185.45	$185.50
Purchase #3	$31.96	5.775%	$33.8057	$33.81	$33.80	$33.80
Purchase #4	$38.54	5.782%	$40.7684	$40.77	$40.75	$40.80
Purchase #5	$105.42	11.727%	$117.7826	$117.78	$117.80	$117.80
Purchase #6	$60.35	10.291%	$66.5606	$66.56	$66.55	$66.60
Purchase #7	$187.89	7.755%	$202.4609	$202.46	$202.45	$202.50
7 purchase totals =	$726.74		$789.5399	$789.55	$789.50	$789.70