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	$79.69	12.322%	$89.5094	$89.51	$89.50	$89.50
Purchase #2	$137.51	5.732%	$145.3921	$145.39	$145.40	$145.40
Purchase #3	$127.44	3.700%	$132.1553	$132.16	$132.15	$132.20
Purchase #4	$134.57	13.768%	$153.0976	$153.10	$153.10	$153.10
Purchase #5	$152.81	12.104%	$171.3061	$171.31	$171.30	$171.30
Purchase #6	$57.98	3.315%	$59.902	$59.90	$59.90	$59.90
Purchase #7	$152.31	9.713%	$167.1039	$167.10	$167.10	$167.10
7 purchase totals =	$842.31		$918.4664	$918.47	$918.45	$918.50