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	$61.99	10.762%	$68.6614	$68.66	$68.65	$68.70
Purchase #2	$32.91	13.347%	$37.3025	$37.30	$37.30	$37.30
Purchase #3	$123.37	12.681%	$139.0145	$139.01	$139.00	$139.00
Purchase #4	$26.87	3.868%	$27.9093	$27.91	$27.90	$27.90
Purchase #5	$52.79	12.220%	$59.2409	$59.24	$59.25	$59.20
Purchase #6	$245.64	4.161%	$255.8611	$255.86	$255.85	$255.90
Purchase #7	$171.85	11.253%	$191.1883	$191.19	$191.20	$191.20
7 purchase totals =	$715.42		$779.1780	$779.17	$779.15	$779.20