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	$131.62	5.307%	$138.6051	$138.61	$138.60	$138.60
Purchase #2	$130.59	11.172%	$145.1795	$145.18	$145.20	$145.20
Purchase #3	$55.88	4.596%	$58.4482	$58.45	$58.45	$58.40
Purchase #4	$57.34	9.741%	$62.9255	$62.93	$62.95	$62.90
Purchase #5	$156.89	8.182%	$169.7267	$169.73	$169.75	$169.70
Purchase #6	$139.82	9.354%	$152.8988	$152.90	$152.90	$152.90
Purchase #7	$113.45	9.272%	$123.9691	$123.97	$123.95	$124.00
7 purchase totals =	$785.59		$851.7529	$851.77	$851.80	$851.70