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	$53.52	12.855%	$60.4	$60.40	$60.40	$60.40
Purchase #2	$112.32	7.620%	$120.8788	$120.88	$120.90	$120.90
Purchase #3	$161.64	10.206%	$178.137	$178.14	$178.15	$178.10
Purchase #4	$208.97	9.333%	$228.4732	$228.47	$228.45	$228.50
Purchase #5	$75.57	3.320%	$78.0789	$78.08	$78.10	$78.10
Purchase #6	$36.38	12.423%	$40.8995	$40.90	$40.90	$40.90
Purchase #7	$174.98	11.690%	$195.4352	$195.44	$195.45	$195.40
7 purchase totals =	$823.38		$902.3026	$902.31	$902.35	$902.30