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	$17.54	12.789%	$19.7832	$19.78	$19.80	$19.80
Purchase #2	$209.92	6.356%	$223.2625	$223.26	$223.25	$223.30
Purchase #3	$145.85	9.772%	$160.1025	$160.10	$160.10	$160.10
Purchase #4	$182.85	5.471%	$192.8537	$192.85	$192.85	$192.90
Purchase #5	$142.44	9.610%	$156.1285	$156.13	$156.15	$156.10
Purchase #6	$59.28	11.115%	$65.869	$65.87	$65.85	$65.90
Purchase #7	$223.44	3.805%	$231.9419	$231.94	$231.95	$231.90
7 purchase totals =	$981.32		$1,049.9413	$1,049.93	$1,049.95	$1,050.00