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	$91.35	5.842%	$96.6867	$96.69	$96.70	$96.70
Purchase #2	$127.52	12.636%	$143.6334	$143.63	$143.65	$143.60
Purchase #3	$80.66	3.562%	$83.5331	$83.53	$83.55	$83.50
Purchase #4	$38.34	11.867%	$42.8898	$42.89	$42.90	$42.90
Purchase #5	$50.50	13.500%	$57.3175	$57.32	$57.30	$57.30
Purchase #6	$213.48	11.750%	$238.5639	$238.56	$238.55	$238.60
Purchase #7	$112.65	12.195%	$126.3877	$126.39	$126.40	$126.40
7 purchase totals =	$714.50		$789.0121	$789.01	$789.05	$789.00