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	$243.46	13.617%	$276.6119	$276.61	$276.60	$276.60
Purchase #2	$167.34	6.402%	$178.0531	$178.05	$178.05	$178.10
Purchase #3	$41.27	10.218%	$45.487	$45.49	$45.50	$45.50
Purchase #4	$56.61	6.344%	$60.2013	$60.20	$60.20	$60.20
Purchase #5	$65.78	11.584%	$73.4	$73.40	$73.40	$73.40
Purchase #6	$84.85	8.553%	$92.1072	$92.11	$92.10	$92.10
Purchase #7	$56.63	4.405%	$59.1246	$59.12	$59.10	$59.10
7 purchase totals =	$715.94		$784.9851	$784.98	$784.95	$785.00