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	$137.42	7.708%	$148.0123	$148.01	$148.00	$148.00
Purchase #2	$56.44	11.134%	$62.724	$62.72	$62.70	$62.70
Purchase #3	$233.88	9.260%	$255.5373	$255.54	$255.55	$255.50
Purchase #4	$117.60	9.468%	$128.7344	$128.73	$128.75	$128.70
Purchase #5	$112.99	12.850%	$127.5092	$127.51	$127.50	$127.50
Purchase #6	$239.88	3.531%	$248.3502	$248.35	$248.35	$248.40
Purchase #7	$43.59	3.491%	$45.1117	$45.11	$45.10	$45.10
7 purchase totals =	$941.80		$1,015.9791	$1,015.97	$1,015.95	$1,015.90