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	$109.31	12.770%	$123.2689	$123.27	$123.25	$123.30
Purchase #2	$188.69	11.301%	$210.0139	$210.01	$210.00	$210.00
Purchase #3	$119.55	4.272%	$124.6572	$124.66	$124.65	$124.70
Purchase #4	$54.89	7.693%	$59.1127	$59.11	$59.10	$59.10
Purchase #5	$96.87	13.488%	$109.9358	$109.94	$109.95	$109.90
Purchase #6	$47.97	10.316%	$52.9186	$52.92	$52.90	$52.90
Purchase #7	$94.88	11.763%	$106.0407	$106.04	$106.05	$106.00
7 purchase totals =	$712.16		$785.9478	$785.95	$785.90	$785.90