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	$111.96	11.176%	$124.4726	$124.47	$124.45	$124.50
Purchase #2	$226.47	9.360%	$247.6676	$247.67	$247.65	$247.70
Purchase #3	$30.82	13.643%	$35.0248	$35.02	$35.00	$35.00
Purchase #4	$135.42	4.438%	$141.4299	$141.43	$141.45	$141.40
Purchase #5	$134.35	10.384%	$148.3009	$148.30	$148.30	$148.30
Purchase #6	$125.34	5.194%	$131.8502	$131.85	$131.85	$131.90
Purchase #7	$95.69	5.418%	$100.8745	$100.87	$100.85	$100.90
7 purchase totals =	$860.05		$929.6205	$929.61	$929.55	$929.70