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	$11.69	10.850%	$12.9584	$12.96	$12.95	$13.00
Purchase #2	$173.61	5.114%	$182.4884	$182.49	$182.50	$182.50
Purchase #3	$82.61	3.608%	$85.5906	$85.59	$85.60	$85.60
Purchase #4	$246.99	7.653%	$265.8921	$265.89	$265.90	$265.90
Purchase #5	$151.32	11.415%	$168.5932	$168.59	$168.60	$168.60
Purchase #6	$139.40	5.318%	$146.8133	$146.81	$146.80	$146.80
Purchase #7	$238.52	13.328%	$270.3099	$270.31	$270.30	$270.30
7 purchase totals =	$1,044.14		$1,132.6459	$1,132.64	$1,132.65	$1,132.70