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	$141.36	11.422%	$157.5061	$157.51	$157.50	$157.50
Purchase #2	$149.71	8.597%	$162.5806	$162.58	$162.60	$162.60
Purchase #3	$165.78	11.803%	$185.347	$185.35	$185.35	$185.30
Purchase #4	$212.71	5.208%	$223.7879	$223.79	$223.80	$223.80
Purchase #5	$71.99	9.574%	$78.8823	$78.88	$78.90	$78.90
Purchase #6	$33.72	9.194%	$36.8202	$36.82	$36.80	$36.80
Purchase #7	$144.89	7.393%	$155.6017	$155.60	$155.60	$155.60
7 purchase totals =	$920.16		$1,000.5258	$1,000.53	$1,000.55	$1,000.50