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	$226.33	5.416%	$238.588	$238.59	$238.60	$238.60
Purchase #2	$48.39	10.267%	$53.3582	$53.36	$53.35	$53.40
Purchase #3	$206.74	7.406%	$222.0512	$222.05	$222.05	$222.10
Purchase #4	$245.74	5.272%	$258.6954	$258.70	$258.70	$258.70
Purchase #5	$58.96	13.445%	$66.8872	$66.89	$66.90	$66.90
Purchase #6	$31.52	10.427%	$34.8066	$34.81	$34.80	$34.80
Purchase #7	$73.98	11.256%	$82.3072	$82.31	$82.30	$82.30
7 purchase totals =	$891.66		$956.6938	$956.71	$956.70	$956.80