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	$53.93	4.610%	$56.4162	$56.42	$56.40	$56.40
Purchase #2	$49.25	10.124%	$54.2361	$54.24	$54.25	$54.20
Purchase #3	$140.55	9.550%	$153.9725	$153.97	$153.95	$154.00
Purchase #4	$79.59	7.556%	$85.6038	$85.60	$85.60	$85.60
Purchase #5	$85.65	10.391%	$94.5499	$94.55	$94.55	$94.50
Purchase #6	$122.52	7.610%	$131.8438	$131.84	$131.85	$131.80
Purchase #7	$94.88	5.312%	$99.92	$99.92	$99.90	$99.90
7 purchase totals =	$626.37		$676.5423	$676.54	$676.50	$676.40