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	$136.53	11.456%	$152.1709	$152.17	$152.15	$152.20
Purchase #2	$236.63	4.581%	$247.47	$247.47	$247.45	$247.50
Purchase #3	$38.63	5.418%	$40.723	$40.72	$40.70	$40.70
Purchase #4	$141.79	6.767%	$151.3849	$151.38	$151.40	$151.40
Purchase #5	$128.76	3.139%	$132.8018	$132.80	$132.80	$132.80
Purchase #6	$62.65	4.656%	$65.567	$65.57	$65.55	$65.60
Purchase #7	$239.62	7.818%	$258.3535	$258.35	$258.35	$258.40
7 purchase totals =	$984.61		$1,048.4711	$1,048.46	$1,048.40	$1,048.60