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	$26.26	9.868%	$28.8513	$28.85	$28.85	$28.90
Purchase #2	$13.86	6.399%	$14.7469	$14.75	$14.75	$14.70
Purchase #3	$140.52	11.521%	$156.7093	$156.71	$156.70	$156.70
Purchase #4	$65.29	11.711%	$72.9361	$72.94	$72.95	$72.90
Purchase #5	$205.70	5.377%	$216.7605	$216.76	$216.75	$216.80
Purchase #6	$174.46	10.376%	$192.562	$192.56	$192.55	$192.60
Purchase #7	$104.57	6.335%	$111.1945	$111.19	$111.20	$111.20
7 purchase totals =	$730.66		$793.7606	$793.76	$793.75	$793.80