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	$80.96	4.407%	$84.5279	$84.53	$84.55	$84.50
Purchase #2	$61.27	6.602%	$65.315	$65.32	$65.30	$65.30
Purchase #3	$167.50	13.467%	$190.0572	$190.06	$190.05	$190.10
Purchase #4	$223.89	11.803%	$250.3157	$250.32	$250.30	$250.30
Purchase #5	$127.33	9.131%	$138.9565	$138.96	$138.95	$139.00
Purchase #6	$213.97	5.432%	$225.5929	$225.59	$225.60	$225.60
Purchase #7	$84.70	11.115%	$94.1144	$94.11	$94.10	$94.10
7 purchase totals =	$959.62		$1,048.8796	$1,048.89	$1,048.85	$1,048.90