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	$47.38	7.828%	$51.0889	$51.09	$51.10	$51.10
Purchase #2	$245.25	13.695%	$278.837	$278.84	$278.85	$278.80
Purchase #3	$97.93	5.654%	$103.467	$103.47	$103.45	$103.50
Purchase #4	$42.34	3.276%	$43.7271	$43.73	$43.75	$43.70
Purchase #5	$70.74	3.307%	$73.0794	$73.08	$73.10	$73.10
Purchase #6	$119.78	9.605%	$131.2849	$131.28	$131.30	$131.30
Purchase #7	$53.48	10.276%	$58.9756	$58.98	$59.00	$59.00
7 purchase totals =	$676.90		$740.4599	$740.47	$740.55	$740.50