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	$19.45	8.540%	$21.111	$21.11	$21.10	$21.10
Purchase #2	$232.63	9.353%	$254.3879	$254.39	$254.40	$254.40
Purchase #3	$163.87	13.369%	$185.7778	$185.78	$185.80	$185.80
Purchase #4	$73.83	6.358%	$78.5241	$78.52	$78.50	$78.50
Purchase #5	$12.82	6.597%	$13.6657	$13.67	$13.65	$13.70
Purchase #6	$250.41	12.483%	$281.6687	$281.67	$281.65	$281.70
Purchase #7	$93.55	6.760%	$99.874	$99.87	$99.85	$99.90
7 purchase totals =	$846.56		$935.0092	$935.01	$934.95	$935.10