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	$15.87	3.118%	$16.3648	$16.36	$16.35	$16.40
Purchase #2	$104.78	12.606%	$117.9886	$117.99	$118.00	$118.00
Purchase #3	$109.34	12.867%	$123.4088	$123.41	$123.40	$123.40
Purchase #4	$170.28	4.621%	$178.1486	$178.15	$178.15	$178.10
Purchase #5	$91.54	4.315%	$95.49	$95.49	$95.50	$95.50
Purchase #6	$173.56	13.474%	$196.9455	$196.95	$196.95	$196.90
Purchase #7	$79.47	12.511%	$89.4125	$89.41	$89.40	$89.40
7 purchase totals =	$744.84		$817.7588	$817.76	$817.75	$817.70