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	$45.38	12.636%	$51.1142	$51.11	$51.10	$51.10
Purchase #2	$38.40	4.102%	$39.9752	$39.98	$40.00	$40.00
Purchase #3	$140.81	3.803%	$146.165	$146.17	$146.15	$146.20
Purchase #4	$173.30	10.523%	$191.5364	$191.54	$191.55	$191.50
Purchase #5	$213.90	10.531%	$236.4258	$236.43	$236.45	$236.40
Purchase #6	$206.66	4.190%	$215.3191	$215.32	$215.30	$215.30
Purchase #7	$38.98	8.214%	$42.1818	$42.18	$42.20	$42.20
7 purchase totals =	$857.43		$922.7175	$922.73	$922.75	$922.70