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	$52.93	7.806%	$57.0617	$57.06	$57.05	$57.10
Purchase #2	$13.61	13.210%	$15.4079	$15.41	$15.40	$15.40
Purchase #3	$133.96	7.542%	$144.0633	$144.06	$144.05	$144.10
Purchase #4	$95.43	13.696%	$108.5001	$108.50	$108.50	$108.50
Purchase #5	$134.74	5.837%	$142.6048	$142.60	$142.60	$142.60
Purchase #6	$40.69	11.837%	$45.5065	$45.51	$45.50	$45.50
Purchase #7	$139.64	6.492%	$148.7054	$148.71	$148.70	$148.70
7 purchase totals =	$611.00		$661.8497	$661.85	$661.80	$661.90