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	$34.78	11.324%	$38.7185	$38.72	$38.70	$38.70
Purchase #2	$158.44	12.491%	$178.2307	$178.23	$178.25	$178.20
Purchase #3	$146.86	13.399%	$166.5378	$166.54	$166.55	$166.50
Purchase #4	$79.39	5.227%	$83.5397	$83.54	$83.55	$83.50
Purchase #5	$152.30	5.668%	$160.9324	$160.93	$160.95	$160.90
Purchase #6	$216.33	7.422%	$232.386	$232.39	$232.40	$232.40
Purchase #7	$213.77	4.280%	$222.9194	$222.92	$222.90	$222.90
7 purchase totals =	$1,001.87		$1,083.2645	$1,083.27	$1,083.30	$1,083.10