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	$129.45	7.751%	$139.4837	$139.48	$139.50	$139.50
Purchase #2	$131.76	9.128%	$143.7871	$143.79	$143.80	$143.80
Purchase #3	$172.87	6.381%	$183.9008	$183.90	$183.90	$183.90
Purchase #4	$85.29	8.416%	$92.468	$92.47	$92.45	$92.50
Purchase #5	$20.50	4.631%	$21.4494	$21.45	$21.45	$21.40
Purchase #6	$64.35	4.850%	$67.471	$67.47	$67.45	$67.50
Purchase #7	$221.34	11.280%	$246.3072	$246.31	$246.30	$246.30
7 purchase totals =	$825.56		$894.8672	$894.87	$894.85	$894.90