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	$10.40	10.191%	$11.4599	$11.46	$11.45	$11.50
Purchase #2	$72.63	7.331%	$77.9545	$77.95	$77.95	$78.00
Purchase #3	$51.98	8.771%	$56.5392	$56.54	$56.55	$56.50
Purchase #4	$86.98	13.586%	$98.7971	$98.80	$98.80	$98.80
Purchase #5	$25.93	7.323%	$27.8289	$27.83	$27.85	$27.80
Purchase #6	$54.58	3.451%	$56.4636	$56.46	$56.45	$56.50
Purchase #7	$243.57	8.330%	$263.8594	$263.86	$263.85	$263.90
7 purchase totals =	$546.07		$592.9026	$592.90	$592.90	$593.00