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	$103.82	5.557%	$109.5893	$109.59	$109.60	$109.60
Purchase #2	$157.31	4.396%	$164.2253	$164.23	$164.25	$164.20
Purchase #3	$157.76	11.366%	$175.691	$175.69	$175.70	$175.70
Purchase #4	$98.96	6.162%	$105.0579	$105.06	$105.05	$105.10
Purchase #5	$13.29	7.642%	$14.3056	$14.31	$14.30	$14.30
Purchase #6	$155.34	8.359%	$168.3249	$168.32	$168.30	$168.30
Purchase #7	$228.65	6.357%	$243.1853	$243.19	$243.20	$243.20
7 purchase totals =	$915.13		$980.3793	$980.39	$980.40	$980.40