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	$43.97	8.648%	$47.7725	$47.77	$47.75	$47.80
Purchase #2	$141.39	6.432%	$150.4842	$150.48	$150.50	$150.50
Purchase #3	$83.66	8.251%	$90.5628	$90.56	$90.55	$90.60
Purchase #4	$106.41	5.180%	$111.922	$111.92	$111.90	$111.90
Purchase #5	$47.63	10.637%	$52.6964	$52.70	$52.70	$52.70
Purchase #6	$89.97	9.349%	$98.3813	$98.38	$98.40	$98.40
Purchase #7	$123.49	3.717%	$128.0801	$128.08	$128.10	$128.10
7 purchase totals =	$636.52		$679.8993	$679.89	$679.90	$680.00