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	$127.97	11.693%	$142.9335	$142.93	$142.95	$142.90
Purchase #2	$231.63	7.373%	$248.7081	$248.71	$248.70	$248.70
Purchase #3	$152.34	4.464%	$159.1405	$159.14	$159.15	$159.10
Purchase #4	$236.73	9.657%	$259.591	$259.59	$259.60	$259.60
Purchase #5	$240.42	7.521%	$258.502	$258.50	$258.50	$258.50
Purchase #6	$18.75	9.304%	$20.4945	$20.49	$20.50	$20.50
Purchase #7	$10.32	11.395%	$11.496	$11.50	$11.50	$11.50
7 purchase totals =	$1,018.16		$1,100.8656	$1,100.86	$1,100.90	$1,100.80