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	$164.40	4.119%	$171.1716	$171.17	$171.15	$171.20
Purchase #2	$98.78	6.471%	$105.1721	$105.17	$105.15	$105.20
Purchase #3	$168.71	11.595%	$188.2719	$188.27	$188.25	$188.30
Purchase #4	$99.98	4.743%	$104.7221	$104.72	$104.70	$104.70
Purchase #5	$110.66	10.852%	$122.6688	$122.67	$122.65	$122.70
Purchase #6	$94.53	6.724%	$100.8862	$100.89	$100.90	$100.90
Purchase #7	$180.63	5.824%	$191.1499	$191.15	$191.15	$191.10
7 purchase totals =	$917.69		$984.0426	$984.04	$983.95	$984.10