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	$238.97	13.441%	$271.09	$271.09	$271.10	$271.10
Purchase #2	$74.82	7.430%	$80.3791	$80.38	$80.40	$80.40
Purchase #3	$85.37	6.471%	$90.8943	$90.89	$90.90	$90.90
Purchase #4	$41.25	11.206%	$45.8725	$45.87	$45.85	$45.90
Purchase #5	$133.38	9.124%	$145.5496	$145.55	$145.55	$145.50
Purchase #6	$138.53	6.157%	$147.0593	$147.06	$147.05	$147.10
Purchase #7	$91.45	3.467%	$94.6206	$94.62	$94.60	$94.60
7 purchase totals =	$803.77		$875.4654	$875.46	$875.45	$875.50