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	$244.97	12.794%	$276.3115	$276.31	$276.30	$276.30
Purchase #2	$48.35	11.178%	$53.7546	$53.75	$53.75	$53.80
Purchase #3	$155.54	3.118%	$160.3897	$160.39	$160.40	$160.40
Purchase #4	$141.41	13.648%	$160.7096	$160.71	$160.70	$160.70
Purchase #5	$48.53	9.444%	$53.1132	$53.11	$53.10	$53.10
Purchase #6	$78.88	3.685%	$81.7867	$81.79	$81.80	$81.80
Purchase #7	$13.33	11.801%	$14.9031	$14.90	$14.90	$14.90
7 purchase totals =	$731.01		$800.9684	$800.96	$800.95	$801.00