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	$59.28	12.801%	$66.8684	$66.87	$66.85	$66.90
Purchase #2	$52.94	6.326%	$56.289	$56.29	$56.30	$56.30
Purchase #3	$195.62	13.859%	$222.731	$222.73	$222.75	$222.70
Purchase #4	$31.56	3.347%	$32.6163	$32.62	$32.60	$32.60
Purchase #5	$125.49	10.681%	$138.8936	$138.89	$138.90	$138.90
Purchase #6	$232.26	10.289%	$256.1572	$256.16	$256.15	$256.20
Purchase #7	$213.61	4.240%	$222.6671	$222.67	$222.65	$222.70
7 purchase totals =	$910.76		$996.2226	$996.23	$996.20	$996.30