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	$7.73	8.359%	$8.3762	$8.38	$8.40	$8.40
Purchase #2	$216.63	10.849%	$240.1322	$240.13	$240.15	$240.10
Purchase #3	$53.94	10.313%	$59.5028	$59.50	$59.50	$59.50
Purchase #4	$167.28	4.581%	$174.9431	$174.94	$174.95	$174.90
Purchase #5	$213.55	7.435%	$229.4274	$229.43	$229.45	$229.40
Purchase #6	$52.77	3.617%	$54.6787	$54.68	$54.70	$54.70
Purchase #7	$15.92	13.704%	$18.1017	$18.10	$18.10	$18.10
7 purchase totals =	$727.82		$785.1621	$785.16	$785.25	$785.10