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	$50.64	12.353%	$56.8956	$56.90	$56.90	$56.90
Purchase #2	$186.43	4.366%	$194.5695	$194.57	$194.55	$194.60
Purchase #3	$210.93	12.846%	$238.0261	$238.03	$238.05	$238.00
Purchase #4	$68.91	4.849%	$72.2514	$72.25	$72.25	$72.30
Purchase #5	$105.98	9.777%	$116.3417	$116.34	$116.35	$116.30
Purchase #6	$160.35	13.758%	$182.411	$182.41	$182.40	$182.40
Purchase #7	$48.77	7.613%	$52.4829	$52.48	$52.50	$52.50
7 purchase totals =	$832.01		$912.9782	$912.98	$913.00	$913.00