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	$127.68	12.627%	$143.8022	$143.80	$143.80	$143.80
Purchase #2	$141.30	6.110%	$149.9334	$149.93	$149.95	$149.90
Purchase #3	$79.73	7.790%	$85.941	$85.94	$85.95	$85.90
Purchase #4	$122.44	4.666%	$128.1531	$128.15	$128.15	$128.20
Purchase #5	$245.67	12.709%	$276.8922	$276.89	$276.90	$276.90
Purchase #6	$247.30	13.400%	$280.4382	$280.44	$280.45	$280.40
Purchase #7	$41.25	6.254%	$43.8298	$43.83	$43.85	$43.80
7 purchase totals =	$1,005.37		$1,108.9899	$1,108.98	$1,109.05	$1,108.90