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	$71.94	9.241%	$78.588	$78.59	$78.60	$78.60
Purchase #2	$202.56	9.360%	$221.5196	$221.52	$221.50	$221.50
Purchase #3	$203.77	9.723%	$223.5826	$223.58	$223.60	$223.60
Purchase #4	$83.99	9.344%	$91.838	$91.84	$91.85	$91.80
Purchase #5	$105.38	8.460%	$114.2951	$114.30	$114.30	$114.30
Purchase #6	$135.86	7.807%	$146.4666	$146.47	$146.45	$146.50
Purchase #7	$103.35	5.255%	$108.781	$108.78	$108.80	$108.80
7 purchase totals =	$906.85		$985.0709	$985.08	$985.10	$985.10