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	$200.52	3.524%	$207.5863	$207.59	$207.60	$207.60
Purchase #2	$13.90	8.563%	$15.0903	$15.09	$15.10	$15.10
Purchase #3	$199.66	9.603%	$218.8333	$218.83	$218.85	$218.80
Purchase #4	$138.28	3.711%	$143.4116	$143.41	$143.40	$143.40
Purchase #5	$68.58	4.421%	$71.6119	$71.61	$71.60	$71.60
Purchase #6	$69.69	5.362%	$73.4268	$73.43	$73.45	$73.40
Purchase #7	$72.70	7.487%	$78.143	$78.14	$78.15	$78.10
7 purchase totals =	$763.33		$808.1032	$808.10	$808.15	$808.00