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	$61.51	5.299%	$64.7694	$64.77	$64.75	$64.80
Purchase #2	$84.51	6.541%	$90.0378	$90.04	$90.05	$90.00
Purchase #3	$140.30	10.775%	$155.4173	$155.42	$155.40	$155.40
Purchase #4	$123.50	10.733%	$136.7553	$136.76	$136.75	$136.80
Purchase #5	$179.98	10.376%	$198.6547	$198.65	$198.65	$198.70
Purchase #6	$137.53	3.443%	$142.2652	$142.27	$142.25	$142.30
Purchase #7	$39.28	11.868%	$43.9418	$43.94	$43.95	$43.90
7 purchase totals =	$766.61		$831.8415	$831.85	$831.80	$831.90