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	$206.91	7.846%	$223.1442	$223.14	$223.15	$223.10
Purchase #2	$215.78	3.359%	$223.0281	$223.03	$223.05	$223.00
Purchase #3	$228.30	9.713%	$250.4748	$250.47	$250.45	$250.50
Purchase #4	$163.47	11.196%	$181.7721	$181.77	$181.75	$181.80
Purchase #5	$117.48	8.839%	$127.8641	$127.86	$127.85	$127.90
Purchase #6	$74.46	8.775%	$80.9939	$80.99	$81.00	$81.00
Purchase #7	$51.50	6.857%	$55.0314	$55.03	$55.05	$55.00
7 purchase totals =	$1,057.90		$1,142.3086	$1,142.29	$1,142.30	$1,142.30