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	$6.92	8.675%	$7.5203	$7.52	$7.50	$7.50
Purchase #2	$102.97	3.630%	$106.7078	$106.71	$106.70	$106.70
Purchase #3	$144.83	13.569%	$164.482	$164.48	$164.50	$164.50
Purchase #4	$94.31	11.695%	$105.3396	$105.34	$105.35	$105.30
Purchase #5	$57.37	3.822%	$59.5627	$59.56	$59.55	$59.60
Purchase #6	$176.68	7.398%	$189.7508	$189.75	$189.75	$189.80
Purchase #7	$233.91	7.783%	$252.1152	$252.12	$252.10	$252.10
7 purchase totals =	$816.99		$885.4784	$885.48	$885.45	$885.50