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	$67.51	6.780%	$72.0872	$72.09	$72.10	$72.10
Purchase #2	$90.81	8.591%	$98.6115	$98.61	$98.60	$98.60
Purchase #3	$232.66	3.796%	$241.4918	$241.49	$241.50	$241.50
Purchase #4	$32.96	6.690%	$35.165	$35.17	$35.15	$35.20
Purchase #5	$38.88	5.767%	$41.1222	$41.12	$41.10	$41.10
Purchase #6	$35.40	5.215%	$37.2461	$37.25	$37.25	$37.20
Purchase #7	$10.39	9.168%	$11.3426	$11.34	$11.35	$11.30
7 purchase totals =	$508.61		$537.0664	$537.07	$537.05	$537.00