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	$40.96	12.203%	$45.9583	$45.96	$45.95	$46.00
Purchase #2	$57.89	6.254%	$61.5104	$61.51	$61.50	$61.50
Purchase #3	$203.52	9.538%	$222.9317	$222.93	$222.95	$222.90
Purchase #4	$116.25	3.539%	$120.3641	$120.36	$120.35	$120.40
Purchase #5	$44.97	5.429%	$47.4114	$47.41	$47.40	$47.40
Purchase #6	$53.53	12.799%	$60.3813	$60.38	$60.40	$60.40
Purchase #7	$100.81	13.342%	$114.2601	$114.26	$114.25	$114.30
7 purchase totals =	$617.93		$672.8173	$672.81	$672.80	$672.90