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	$199.68	10.791%	$221.2275	$221.23	$221.25	$221.20
Purchase #2	$145.81	3.308%	$150.6334	$150.63	$150.65	$150.60
Purchase #3	$238.80	8.572%	$259.2699	$259.27	$259.25	$259.30
Purchase #4	$225.61	7.641%	$242.8489	$242.85	$242.85	$242.80
Purchase #5	$78.35	13.458%	$88.8943	$88.89	$88.90	$88.90
Purchase #6	$10.75	13.868%	$12.2408	$12.24	$12.25	$12.20
Purchase #7	$24.78	3.654%	$25.6855	$25.69	$25.70	$25.70
7 purchase totals =	$923.78		$1,000.8003	$1,000.80	$1,000.85	$1,000.70