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	$76.61	9.417%	$83.8244	$83.82	$83.80	$83.80
Purchase #2	$240.27	13.238%	$272.0769	$272.08	$272.10	$272.10
Purchase #3	$31.97	7.380%	$34.3294	$34.33	$34.35	$34.30
Purchase #4	$58.88	11.534%	$65.6712	$65.67	$65.65	$65.70
Purchase #5	$164.46	11.592%	$183.5242	$183.52	$183.50	$183.50
Purchase #6	$152.50	12.723%	$171.9026	$171.90	$171.90	$171.90
Purchase #7	$115.31	13.745%	$131.1594	$131.16	$131.15	$131.20
7 purchase totals =	$840.00		$942.4881	$942.48	$942.45	$942.50