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	$121.43	10.556%	$134.2482	$134.25	$134.25	$134.20
Purchase #2	$244.89	4.357%	$255.5599	$255.56	$255.55	$255.60
Purchase #3	$113.28	10.391%	$125.0509	$125.05	$125.05	$125.10
Purchase #4	$14.35	11.207%	$15.9582	$15.96	$15.95	$16.00
Purchase #5	$123.52	7.342%	$132.5888	$132.59	$132.60	$132.60
Purchase #6	$243.90	12.791%	$275.0972	$275.10	$275.10	$275.10
Purchase #7	$143.32	11.511%	$159.8176	$159.82	$159.80	$159.80
7 purchase totals =	$1,004.69		$1,098.3208	$1,098.33	$1,098.30	$1,098.40