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	$20.57	13.763%	$23.401	$23.40	$23.40	$23.40
Purchase #2	$229.38	8.347%	$248.5263	$248.53	$248.55	$248.50
Purchase #3	$196.65	13.473%	$223.1447	$223.14	$223.15	$223.10
Purchase #4	$32.45	9.681%	$35.5915	$35.59	$35.60	$35.60
Purchase #5	$60.80	9.863%	$66.7967	$66.80	$66.80	$66.80
Purchase #6	$54.46	9.524%	$59.6468	$59.65	$59.65	$59.60
Purchase #7	$59.96	13.257%	$67.9089	$67.91	$67.90	$67.90
7 purchase totals =	$654.27		$725.0159	$725.02	$725.05	$724.90