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	$75.46	9.219%	$82.4167	$82.42	$82.40	$82.40
Purchase #2	$99.34	6.390%	$105.6878	$105.69	$105.70	$105.70
Purchase #3	$76.46	12.327%	$85.8852	$85.89	$85.90	$85.90
Purchase #4	$32.86	11.768%	$36.727	$36.73	$36.75	$36.70
Purchase #5	$139.98	8.855%	$152.3752	$152.38	$152.40	$152.40
Purchase #6	$177.67	8.235%	$192.3011	$192.30	$192.30	$192.30
Purchase #7	$65.81	12.162%	$73.8138	$73.81	$73.80	$73.80
7 purchase totals =	$667.58		$729.2068	$729.22	$729.25	$729.20