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	$148.49	13.479%	$168.505	$168.51	$168.50	$168.50
Purchase #2	$113.88	9.556%	$124.7624	$124.76	$124.75	$124.80
Purchase #3	$136.77	4.315%	$142.6716	$142.67	$142.65	$142.70
Purchase #4	$27.49	6.174%	$29.1872	$29.19	$29.20	$29.20
Purchase #5	$197.65	9.240%	$215.9129	$215.91	$215.90	$215.90
Purchase #6	$90.45	8.376%	$98.0261	$98.03	$98.05	$98.00
Purchase #7	$162.61	3.861%	$168.8884	$168.89	$168.90	$168.90
7 purchase totals =	$877.34		$947.9536	$947.96	$947.95	$948.00