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	$232.31	6.851%	$248.2256	$248.23	$248.25	$248.20
Purchase #2	$166.37	9.225%	$181.7176	$181.72	$181.70	$181.70
Purchase #3	$58.52	5.167%	$61.5437	$61.54	$61.55	$61.50
Purchase #4	$31.57	12.357%	$35.4711	$35.47	$35.45	$35.50
Purchase #5	$131.59	9.751%	$144.4213	$144.42	$144.40	$144.40
Purchase #6	$51.27	13.188%	$58.0315	$58.03	$58.05	$58.00
Purchase #7	$197.71	5.854%	$209.2839	$209.28	$209.30	$209.30
7 purchase totals =	$869.34		$938.6947	$938.69	$938.70	$938.60