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	$14.74	11.650%	$16.4572	$16.46	$16.45	$16.50
Purchase #2	$156.75	4.709%	$164.1314	$164.13	$164.15	$164.10
Purchase #3	$104.50	9.307%	$114.2258	$114.23	$114.25	$114.20
Purchase #4	$33.28	11.677%	$37.1661	$37.17	$37.15	$37.20
Purchase #5	$42.40	7.248%	$45.4732	$45.47	$45.45	$45.50
Purchase #6	$158.52	13.478%	$179.8853	$179.89	$179.90	$179.90
Purchase #7	$114.94	12.614%	$129.4385	$129.44	$129.45	$129.40
7 purchase totals =	$625.13		$686.7775	$686.79	$686.80	$686.80