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	$73.33	13.227%	$83.0294	$83.03	$83.05	$83.00
Purchase #2	$192.66	10.829%	$213.5232	$213.52	$213.50	$213.50
Purchase #3	$140.35	11.605%	$156.6376	$156.64	$156.65	$156.60
Purchase #4	$236.45	3.846%	$245.5439	$245.54	$245.55	$245.50
Purchase #5	$162.75	3.397%	$168.2786	$168.28	$168.30	$168.30
Purchase #6	$10.48	9.122%	$11.436	$11.44	$11.45	$11.40
Purchase #7	$39.73	10.568%	$43.9287	$43.93	$43.95	$43.90
7 purchase totals =	$855.75		$922.3774	$922.38	$922.45	$922.20