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	$37.94	6.193%	$40.2896	$40.29	$40.30	$40.30
Purchase #2	$42.38	7.627%	$45.6123	$45.61	$45.60	$45.60
Purchase #3	$220.32	9.259%	$240.7194	$240.72	$240.70	$240.70
Purchase #4	$114.91	12.865%	$129.6932	$129.69	$129.70	$129.70
Purchase #5	$37.98	4.412%	$39.6557	$39.66	$39.65	$39.70
Purchase #6	$99.56	10.182%	$109.6972	$109.70	$109.70	$109.70
Purchase #7	$182.57	3.417%	$188.8084	$188.81	$188.80	$188.80
7 purchase totals =	$735.66		$794.4758	$794.48	$794.45	$794.50