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	$34.25	12.280%	$38.4559	$38.46	$38.45	$38.50
Purchase #2	$216.49	6.660%	$230.9082	$230.91	$230.90	$230.90
Purchase #3	$220.89	10.207%	$243.4362	$243.44	$243.45	$243.40
Purchase #4	$239.31	4.750%	$250.6772	$250.68	$250.70	$250.70
Purchase #5	$46.40	9.835%	$50.9634	$50.96	$50.95	$51.00
Purchase #6	$43.54	6.805%	$46.5029	$46.50	$46.50	$46.50
Purchase #7	$71.75	9.482%	$78.5533	$78.55	$78.55	$78.60
7 purchase totals =	$872.63		$939.4971	$939.50	$939.50	$939.60