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	$205.45	10.213%	$226.4326	$226.43	$226.45	$226.40
Purchase #2	$204.56	9.401%	$223.7907	$223.79	$223.80	$223.80
Purchase #3	$198.33	11.874%	$221.8797	$221.88	$221.90	$221.90
Purchase #4	$62.33	13.280%	$70.6074	$70.61	$70.60	$70.60
Purchase #5	$181.66	5.664%	$191.9492	$191.95	$191.95	$191.90
Purchase #6	$31.50	7.360%	$33.8184	$33.82	$33.80	$33.80
Purchase #7	$29.42	4.256%	$30.6721	$30.67	$30.65	$30.70
7 purchase totals =	$913.25		$999.1501	$999.15	$999.15	$999.10