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	$123.60	10.782%	$136.9266	$136.93	$136.95	$136.90
Purchase #2	$142.38	3.439%	$147.2764	$147.28	$147.30	$147.30
Purchase #3	$50.66	3.121%	$52.2411	$52.24	$52.25	$52.20
Purchase #4	$214.77	6.761%	$229.2906	$229.29	$229.30	$229.30
Purchase #5	$53.67	11.145%	$59.6515	$59.65	$59.65	$59.70
Purchase #6	$117.69	11.746%	$131.5139	$131.51	$131.50	$131.50
Purchase #7	$196.72	9.233%	$214.8832	$214.88	$214.90	$214.90
7 purchase totals =	$899.49		$971.7833	$971.78	$971.85	$971.80