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	$236.51	12.104%	$265.1372	$265.14	$265.15	$265.10
Purchase #2	$124.68	8.168%	$134.8639	$134.86	$134.85	$134.90
Purchase #3	$149.84	7.336%	$160.8323	$160.83	$160.85	$160.80
Purchase #4	$150.96	11.467%	$168.2706	$168.27	$168.25	$168.30
Purchase #5	$147.56	3.432%	$152.6243	$152.62	$152.60	$152.60
Purchase #6	$20.32	4.557%	$21.246	$21.25	$21.25	$21.20
Purchase #7	$168.40	11.565%	$187.8755	$187.88	$187.90	$187.90
7 purchase totals =	$998.27		$1,090.8498	$1,090.85	$1,090.85	$1,090.80