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	$236.76	8.349%	$256.5271	$256.53	$256.55	$256.50
Purchase #2	$156.74	4.792%	$164.251	$164.25	$164.25	$164.30
Purchase #3	$123.91	10.312%	$136.6876	$136.69	$136.70	$136.70
Purchase #4	$249.59	6.488%	$265.7834	$265.78	$265.80	$265.80
Purchase #5	$22.89	8.346%	$24.8004	$24.80	$24.80	$24.80
Purchase #6	$105.44	3.826%	$109.4741	$109.47	$109.45	$109.50
Purchase #7	$167.91	10.733%	$185.9318	$185.93	$185.95	$185.90
7 purchase totals =	$1,063.24		$1,143.4554	$1,143.45	$1,143.50	$1,143.50