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	$171.27	4.397%	$178.8007	$178.80	$178.80	$178.80
Purchase #2	$11.79	13.807%	$13.4178	$13.42	$13.40	$13.40
Purchase #3	$100.80	12.104%	$113.0008	$113.00	$113.00	$113.00
Purchase #4	$84.46	13.145%	$95.5623	$95.56	$95.55	$95.60
Purchase #5	$139.57	11.173%	$155.1642	$155.16	$155.15	$155.20
Purchase #6	$77.53	6.712%	$82.7338	$82.73	$82.75	$82.70
Purchase #7	$173.57	13.331%	$196.7086	$196.71	$196.70	$196.70
7 purchase totals =	$758.99		$835.3882	$835.38	$835.35	$835.40