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	$99.55	3.315%	$102.8501	$102.85	$102.85	$102.90
Purchase #2	$76.65	7.185%	$82.1573	$82.16	$82.15	$82.20
Purchase #3	$95.91	13.412%	$108.7734	$108.77	$108.75	$108.80
Purchase #4	$131.72	12.457%	$148.1284	$148.13	$148.15	$148.10
Purchase #5	$114.64	7.700%	$123.4673	$123.47	$123.45	$123.50
Purchase #6	$87.43	12.555%	$98.4068	$98.41	$98.40	$98.40
Purchase #7	$109.66	6.168%	$116.4238	$116.42	$116.40	$116.40
7 purchase totals =	$715.56		$780.2071	$780.21	$780.15	$780.30