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	$100.80	9.108%	$109.9809	$109.98	$110.00	$110.00
Purchase #2	$34.68	3.363%	$35.8463	$35.85	$35.85	$35.80
Purchase #3	$57.45	11.727%	$64.1872	$64.19	$64.20	$64.20
Purchase #4	$51.79	6.129%	$54.9642	$54.96	$54.95	$55.00
Purchase #5	$80.72	11.284%	$89.8284	$89.83	$89.85	$89.80
Purchase #6	$62.35	6.140%	$66.1783	$66.18	$66.20	$66.20
Purchase #7	$231.90	10.455%	$256.1451	$256.15	$256.15	$256.10
7 purchase totals =	$619.69		$677.1304	$677.14	$677.20	$677.10