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	$40.59	3.724%	$42.1016	$42.10	$42.10	$42.10
Purchase #2	$198.68	6.311%	$211.2187	$211.22	$211.20	$211.20
Purchase #3	$58.29	11.393%	$64.931	$64.93	$64.95	$64.90
Purchase #4	$242.39	7.233%	$259.9221	$259.92	$259.90	$259.90
Purchase #5	$32.98	9.732%	$36.1896	$36.19	$36.20	$36.20
Purchase #6	$100.31	11.245%	$111.5899	$111.59	$111.60	$111.60
Purchase #7	$185.50	7.841%	$200.0451	$200.05	$200.05	$200.00
7 purchase totals =	$858.74		$925.9980	$926.00	$926.00	$925.90