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	$34.78	11.645%	$38.8301	$38.83	$38.85	$38.80
Purchase #2	$194.69	9.869%	$213.904	$213.90	$213.90	$213.90
Purchase #3	$92.86	7.733%	$100.0409	$100.04	$100.05	$100.00
Purchase #4	$154.96	12.627%	$174.5268	$174.53	$174.55	$174.50
Purchase #5	$150.25	3.535%	$155.5613	$155.56	$155.55	$155.60
Purchase #6	$228.61	7.195%	$245.0585	$245.06	$245.05	$245.10
Purchase #7	$206.82	3.204%	$213.4465	$213.45	$213.45	$213.40
7 purchase totals =	$1,062.97		$1,141.3681	$1,141.37	$1,141.40	$1,141.30