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	$139.36	8.727%	$151.5219	$151.52	$151.50	$151.50
Purchase #2	$238.93	11.290%	$265.9052	$265.91	$265.90	$265.90
Purchase #3	$53.53	11.309%	$59.5837	$59.58	$59.60	$59.60
Purchase #4	$94.50	5.201%	$99.4149	$99.41	$99.40	$99.40
Purchase #5	$192.30	13.649%	$218.547	$218.55	$218.55	$218.50
Purchase #6	$11.78	8.737%	$12.8092	$12.81	$12.80	$12.80
Purchase #7	$67.50	5.815%	$71.4251	$71.43	$71.45	$71.40
7 purchase totals =	$797.90		$879.2070	$879.21	$879.20	$879.10