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	$125.87	4.311%	$131.2963	$131.30	$131.30	$131.30
Purchase #2	$218.50	8.790%	$237.7062	$237.71	$237.70	$237.70
Purchase #3	$19.56	4.548%	$20.4496	$20.45	$20.45	$20.40
Purchase #4	$48.98	3.824%	$50.853	$50.85	$50.85	$50.90
Purchase #5	$106.59	4.746%	$111.6488	$111.65	$111.65	$111.60
Purchase #6	$75.49	10.671%	$83.5455	$83.55	$83.55	$83.50
Purchase #7	$147.50	4.158%	$153.6331	$153.63	$153.65	$153.60
7 purchase totals =	$742.49		$789.1325	$789.14	$789.15	$789.00