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	$6.87	7.581%	$7.3908	$7.39	$7.40	$7.40
Purchase #2	$187.74	4.112%	$195.4599	$195.46	$195.45	$195.50
Purchase #3	$76.85	11.388%	$85.6017	$85.60	$85.60	$85.60
Purchase #4	$59.74	13.752%	$67.9554	$67.96	$67.95	$68.00
Purchase #5	$9.39	7.337%	$10.0789	$10.08	$10.10	$10.10
Purchase #6	$29.62	11.786%	$33.111	$33.11	$33.10	$33.10
Purchase #7	$136.40	4.769%	$142.9049	$142.90	$142.90	$142.90
7 purchase totals =	$506.61		$542.5026	$542.50	$542.50	$542.60