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	$151.63	11.172%	$168.5701	$168.57	$168.55	$168.60
Purchase #2	$95.47	3.254%	$98.5766	$98.58	$98.60	$98.60
Purchase #3	$62.63	4.481%	$65.4365	$65.44	$65.45	$65.40
Purchase #4	$95.61	9.728%	$104.9109	$104.91	$104.90	$104.90
Purchase #5	$171.64	8.714%	$186.5967	$186.60	$186.60	$186.60
Purchase #6	$117.98	9.550%	$129.2471	$129.25	$129.25	$129.20
Purchase #7	$86.25	3.773%	$89.5042	$89.50	$89.50	$89.50
7 purchase totals =	$781.21		$842.8421	$842.85	$842.85	$842.80