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	$95.29	5.254%	$100.2965	$100.30	$100.30	$100.30
Purchase #2	$187.80	8.752%	$204.2363	$204.24	$204.25	$204.20
Purchase #3	$97.25	11.665%	$108.5942	$108.59	$108.60	$108.60
Purchase #4	$158.90	9.240%	$173.5824	$173.58	$173.60	$173.60
Purchase #5	$174.90	12.584%	$196.9094	$196.91	$196.90	$196.90
Purchase #6	$28.38	9.601%	$31.1048	$31.10	$31.10	$31.10
Purchase #7	$174.87	9.617%	$191.6872	$191.69	$191.70	$191.70
7 purchase totals =	$917.39		$1,006.4108	$1,006.41	$1,006.45	$1,006.40