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	$124.95	10.838%	$138.4921	$138.49	$138.50	$138.50
Purchase #2	$185.34	8.383%	$200.8771	$200.88	$200.90	$200.90
Purchase #3	$82.56	6.489%	$87.9173	$87.92	$87.90	$87.90
Purchase #4	$62.68	10.171%	$69.0552	$69.06	$69.05	$69.10
Purchase #5	$36.86	5.404%	$38.8519	$38.85	$38.85	$38.90
Purchase #6	$229.33	11.829%	$256.4574	$256.46	$256.45	$256.50
Purchase #7	$72.53	8.671%	$78.8191	$78.82	$78.80	$78.80
7 purchase totals =	$794.25		$870.4701	$870.48	$870.45	$870.60