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	$40.94	3.404%	$42.3336	$42.33	$42.35	$42.30
Purchase #2	$177.36	7.534%	$190.7223	$190.72	$190.70	$190.70
Purchase #3	$188.53	3.840%	$195.7696	$195.77	$195.75	$195.80
Purchase #4	$147.54	8.711%	$160.3922	$160.39	$160.40	$160.40
Purchase #5	$121.98	12.754%	$137.5373	$137.54	$137.55	$137.50
Purchase #6	$16.81	7.397%	$18.0534	$18.05	$18.05	$18.10
Purchase #7	$62.72	7.766%	$67.5908	$67.59	$67.60	$67.60
7 purchase totals =	$755.88		$812.3992	$812.39	$812.40	$812.40