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	$142.45	4.518%	$148.8859	$148.89	$148.90	$148.90
Purchase #2	$69.35	12.653%	$78.1249	$78.12	$78.10	$78.10
Purchase #3	$41.47	5.321%	$43.6766	$43.68	$43.70	$43.70
Purchase #4	$90.84	9.469%	$99.4416	$99.44	$99.45	$99.40
Purchase #5	$248.78	12.263%	$279.2879	$279.29	$279.30	$279.30
Purchase #6	$222.95	11.440%	$248.4555	$248.46	$248.45	$248.50
Purchase #7	$214.79	12.440%	$241.5099	$241.51	$241.50	$241.50
7 purchase totals =	$1,030.63		$1,139.3823	$1,139.39	$1,139.40	$1,139.40