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	$40.70	6.640%	$43.4025	$43.40	$43.40	$43.40
Purchase #2	$140.32	11.716%	$156.7599	$156.76	$156.75	$156.80
Purchase #3	$153.34	12.739%	$172.874	$172.87	$172.85	$172.90
Purchase #4	$65.71	5.287%	$69.1841	$69.18	$69.20	$69.20
Purchase #5	$185.81	5.593%	$196.2024	$196.20	$196.20	$196.20
Purchase #6	$227.59	8.365%	$246.6279	$246.63	$246.65	$246.60
Purchase #7	$90.88	9.603%	$99.6072	$99.61	$99.60	$99.60
7 purchase totals =	$904.35		$984.6580	$984.65	$984.65	$984.70