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	$19.90	4.829%	$20.861	$20.86	$20.85	$20.90
Purchase #2	$16.57	9.137%	$18.084	$18.08	$18.10	$18.10
Purchase #3	$162.55	13.684%	$184.7933	$184.79	$184.80	$184.80
Purchase #4	$174.46	12.357%	$196.018	$196.02	$196.00	$196.00
Purchase #5	$211.30	13.406%	$239.6269	$239.63	$239.65	$239.60
Purchase #6	$71.49	12.725%	$80.5871	$80.59	$80.60	$80.60
Purchase #7	$73.56	13.774%	$83.6922	$83.69	$83.70	$83.70
7 purchase totals =	$729.83		$823.6625	$823.66	$823.70	$823.70