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	$230.25	4.156%	$239.8192	$239.82	$239.80	$239.80
Purchase #2	$86.72	6.404%	$92.2735	$92.27	$92.25	$92.30
Purchase #3	$165.73	6.628%	$176.7146	$176.71	$176.70	$176.70
Purchase #4	$220.44	10.507%	$243.6016	$243.60	$243.60	$243.60
Purchase #5	$175.43	11.500%	$195.6045	$195.60	$195.60	$195.60
Purchase #6	$23.54	7.661%	$25.3434	$25.34	$25.35	$25.30
Purchase #7	$38.27	13.606%	$43.477	$43.48	$43.50	$43.50
7 purchase totals =	$940.38		$1,016.8338	$1,016.82	$1,016.80	$1,016.80