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	$192.70	13.236%	$218.2058	$218.21	$218.20	$218.20
Purchase #2	$248.55	3.221%	$256.5558	$256.56	$256.55	$256.60
Purchase #3	$238.46	7.813%	$257.0909	$257.09	$257.10	$257.10
Purchase #4	$221.42	13.295%	$250.8578	$250.86	$250.85	$250.90
Purchase #5	$93.39	12.781%	$105.3262	$105.33	$105.35	$105.30
Purchase #6	$145.76	9.813%	$160.0634	$160.06	$160.05	$160.10
Purchase #7	$105.93	4.867%	$111.0856	$111.09	$111.10	$111.10
7 purchase totals =	$1,246.21		$1,359.1855	$1,359.20	$1,359.20	$1,359.30