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	$81.43	9.769%	$89.3849	$89.38	$89.40	$89.40
Purchase #2	$29.44	7.837%	$31.7472	$31.75	$31.75	$31.70
Purchase #3	$159.57	7.683%	$171.8298	$171.83	$171.85	$171.80
Purchase #4	$102.46	3.871%	$106.4262	$106.43	$106.45	$106.40
Purchase #5	$215.76	9.316%	$235.8602	$235.86	$235.85	$235.90
Purchase #6	$77.81	10.709%	$86.1427	$86.14	$86.15	$86.10
Purchase #7	$225.72	12.805%	$254.6234	$254.62	$254.60	$254.60
7 purchase totals =	$892.19		$976.0144	$976.01	$976.05	$975.90