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	$35.90	8.803%	$39.0603	$39.06	$39.05	$39.10
Purchase #2	$225.55	11.359%	$251.1702	$251.17	$251.15	$251.20
Purchase #3	$243.83	9.355%	$266.6403	$266.64	$266.65	$266.60
Purchase #4	$174.29	12.800%	$196.5991	$196.60	$196.60	$196.60
Purchase #5	$244.38	4.407%	$255.1498	$255.15	$255.15	$255.10
Purchase #6	$86.29	12.164%	$96.7863	$96.79	$96.80	$96.80
Purchase #7	$29.74	6.840%	$31.7742	$31.77	$31.75	$31.80
7 purchase totals =	$1,039.98		$1,137.1802	$1,137.18	$1,137.15	$1,137.20