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	$74.63	12.845%	$84.2162	$84.22	$84.20	$84.20
Purchase #2	$49.80	12.225%	$55.8881	$55.89	$55.90	$55.90
Purchase #3	$157.69	9.377%	$172.4766	$172.48	$172.50	$172.50
Purchase #4	$31.72	11.494%	$35.3659	$35.37	$35.35	$35.40
Purchase #5	$193.97	8.210%	$209.8949	$209.89	$209.90	$209.90
Purchase #6	$17.59	12.416%	$19.774	$19.77	$19.75	$19.80
Purchase #7	$51.32	10.860%	$56.8934	$56.89	$56.90	$56.90
7 purchase totals =	$576.72		$634.5091	$634.51	$634.50	$634.60