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	$69.58	13.457%	$78.9434	$78.94	$78.95	$78.90
Purchase #2	$39.99	13.668%	$45.4558	$45.46	$45.45	$45.50
Purchase #3	$56.43	4.243%	$58.8243	$58.82	$58.80	$58.80
Purchase #4	$118.28	11.402%	$131.7663	$131.77	$131.75	$131.80
Purchase #5	$51.83	4.517%	$54.1712	$54.17	$54.15	$54.20
Purchase #6	$42.36	8.317%	$45.8831	$45.88	$45.90	$45.90
Purchase #7	$174.65	7.468%	$187.6929	$187.69	$187.70	$187.70
7 purchase totals =	$553.12		$602.7370	$602.73	$602.70	$602.80