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	$75.75	3.773%	$78.608	$78.61	$78.60	$78.60
Purchase #2	$209.83	7.448%	$225.4581	$225.46	$225.45	$225.50
Purchase #3	$44.82	8.365%	$48.5692	$48.57	$48.55	$48.60
Purchase #4	$95.84	13.545%	$108.8215	$108.82	$108.80	$108.80
Purchase #5	$243.58	3.118%	$251.1748	$251.17	$251.15	$251.20
Purchase #6	$64.34	5.457%	$67.851	$67.85	$67.85	$67.90
Purchase #7	$174.57	4.816%	$182.9773	$182.98	$183.00	$183.00
7 purchase totals =	$908.73		$963.4599	$963.46	$963.40	$963.60